2021’s Best Reverse Osmosis Systems | Reviews + Buying Guide: Which Water Filter Is Ideal?

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A proper reverse osmosis system removes almost all contaminants from water, usually at the point of use. The result: Highly pure, healthy, and refreshing drinking water.

Above that, RO systems provide enough filtered water for a whole family. Plus, they’re relatively easy to install and maintain, and cost-effective.

The only problem: How to find a unit that fits your needs? Don’t worry, here’s our collection of the best reverse osmosis systems in 2021.

On This Page You Will…

No Time to Read? Check Our List of the Best Reverse Osmosis Systems!

SystemsOur RatingPriceFilter StagesFiltered WaterNSF StandardsAnnual Cost
AquaTru Reverse Osmosis System

Best Reverse Osmosis Water System: AquaTru

Read Review
$$$41 Gallon in 10-15 Minutes42, 53, 58, 401, P473~$100-120
Use our discount code BOSAquaTru at checkout and get 5% OFF!
Aquasana OptimH2O Under Sink Reverse Osmosis System

Best Under Sink RO System: Aquasana OptimH2O

Read Review
$$4~32 Gallons Per Day42, 53, 58, 401, P473$180-220
Crystal Quest 1000C Under Sink RO System for Well Water

Best RO System for Well Water: Crystal Quest 1000C

Read Review
$$12Up to 50 GPD-$100-155
Crystal Quest Thunder Reverse Osmosis Water Filter System

Our #1 Portable System: Crystal Quest Thunder

Read Review
$$10~50 Gallons Per Day-~$65-100
Waterdrop WD-G3-W RO System

Our #1 Tankless Under Sink RO System: Waterdrop WD-G3-W

Read Review
$$$$30.28 Gallons Per Minute58~$115
NU Aqua Platinum Series 5 Stage Reverse Osmosis System

Cheap Reverse Osmosis System: NU Aqua Platinum Series 5 Stage

Read Review
$5Up to 100 Gallons Per Day-~$50

Best Reverse Osmosis Water Filter Reviews

1. Best Reverse Osmosis System: AquaTru (Including Discount Code!)

In our opinion, the best reverse osmosis system in 2021 is the AquaTru. It’s certified according to official NSF testing standards to remove up to 99.99% of more than 80 water contaminants. In other words, the purified water that comes out of an AquaTru is healthy and safe, and it tastes great!

But this is not even the main reason why we think the AquaTru RO system is the best of its kind. What we love about it is the plug & play functionality. Yep, this countertop unit is completely installation-free – no plumbing, no drilling. This is not only ideal for renters, it also saves you a lot of money if you’re not the kind of person that likes DIY projects. By the way, system maintenance is super simple and low-cost, too. 4.5 stars!

Make sure to use our discount code BOSAquaTru at checkout and get 5% OFF!

AquaTru 4-Stage RO system


System Price:$$$
Filter Stages:4
Purified Water:1 Gallon in 10-15 Minutes
System Certifications:NSF 42, 53, 58, 401, P473

Our Rating

System Pros

  • AquaTru reverse osmosis water filtration system can be set up within a few minutes.
  • Space-saving design.
  • Very easy to use.
    • Clean water collects in removable front tank (great for cooling) and can be dispensed. Contaminants are captured in back tank ready to be discarded.
  • Uses combination of sediment and coconut shell activated carbon pre-filter to trap dust, rust, and other large particles, and adsorb bad tastes and odors as well as chlorine (96.6%) and a bunch of chemicals.
  • Reverse osmosis filter membrane removes heavy metals such as lead (99.1%) and chromium-6 (97.2%), fluoride (93.5%), cyst (99.99%), and TDS (87.1%).
  • Coconut shell activated carbon block post-filter reduces organics, PFOA and PFOS (97.5%), pesticides, pharmaceuticals, etc. Also filters any residual taste.
  • 4-stage filtration process is NSF Standards 42, 53, 58, 401 and Protocol P473 certified.
    • Outstanding test results.
    • Guarantees clean drinking water and the safety of your health.
  • Uses pressure pump to force water through reverse osmosis membrane.
    • Fast filtration: The RO system purifies one gallon of water in 10-15 minutes.
    • Reduces wastewater production. Only 20% of the input water goes down the drain, compared to 3-5 gallons that standard reverse osmosis systems waste for every gallon of filtered water.
  • System maintenance doesn’t require much time or effort thanks to long-lasting filters that can be replaced with a simple twist.
    • AquaTru tracks time and the amount of water used to tell you when you need to change one or more of the filter elements. You’re probably looking at annual/biannual replacements. Cost? Around $100-120 per year which is affordable compared to the competition.
  • All plastic is BPA and BPS-free.
  • Everything is covered by warranty for one year.

System Cons

  • Potential leaking due to design flaw.
  • Some reviewers said their system malfunctioned after a couple of months use.

→ Detailed AquaTru Water Filter Review

2. Best Under Sink Reverse Osmosis System: Aquasana OptimH2O (with Remineralization!)

In our opinion, the best under sink reverse osmosis system in 2021 is the Aquasana OptimH2O. Just like the AquaTru, it’s NSF certified to filter more than 80 water contaminants including chlorine/chloramine (97.66%), mercury (>95.8%), lead (99.3%), VOCs (~99.4%), pentavalent arsenic (97.6%), chromium-6 (97.0%), fluoride (95.7%), overall TDS (95%), BPA (98.9%) and other chemicals, and PFOA & PFOS (96%).

Apart from effective contaminant removal which makes the water safe to drink, the Aquasana OptimH2O RO system also releases healthy calcium, potassium, and magnesium for improved taste and alkalinity.

Did we mention the affordable price and Aquasana’s reliable customer service? Bottom line: 4.5 stars!

Aquasana OptimH2O Under Sink Reverse Osmosis System

Aquasana OptimH2O Under Sink Reverse Osmosis Water Filtration System

System Price:$$
Filter Stages:4
Purified Water:32 Gallons Per Day (GPD)
System Certifications:NSF 42, 53, 58, 401, P473

Our Rating

System Pros

  • Price is fair.
  • Most people are more than happy with their purchase.
  • 3-stage system removes 88+ contaminants from water.
    • Full system is certified according to NSF/ANSI standards 42, 53, 58, 401, and P473 for guaranteed performance.
  • Uses activated carbon filter to eliminate chlorine and larger particulates.
  • RO membrane filters out heavy metals, microorganisms, and many other potentially harmful contaminants.
  • Claryum (filter stage 3) combines activated with catalytic carbon to adsorb pesticides, herbicides, chloramine, a bunch of heavy metals, drug residues, etc.
  • Additional remineralization stage enriches water with healthy calcium, magnesium, and potassium to improve taste and balance pH.
  • 32 gallons daily filtration capacity is enough water for regular household use.
    • Recommended operating water pressure: 40-100 psi.
  • 3 full-metal faucet designs to choose from: Chrome, brushed nickel, and oil-rubbed bronze.
  • RO system can be DIY-installed. All required parts + step-by-step installation instructions are included in the package.
    • Just make sure to follow every single step as disclosed in the manual. Contact customer service if you don’t know what to do next.
  • Aquasana OptimH2O reverse osmosis system is easy to maintain thanks to twist on/off filter housings and quick-connect fittings. Annual replacement filter cost: About $180-220 depending on water quality and usage.
    • More than what you pay with most of the competition.
    • Join the Water for Life filter program to get discount.
  • RO system is covered by 2-year limited warranty + 90-day satisfaction guarantee for peace of mind.

System Cons

  • A few people had problems with leaking.
    • Aquasana sends replacement parts free of charge.
  • Issues with overall quality, especially water dispenser which feels flimsy.
  • Relatively slow flow rate.

→ Read Our Full Aquasana OptimH2O Review Here

3. Best Reverse Osmosis System for Well Water (Optional UV): Crystal Quest 1000C & 1000CP

In our opinion, the best RO system for well water in 2021 is the Crystal Quest 1000C respectively the 1000CP. The only difference is that the latter comes with a pump in case your water is high in TDS or you don’t have enough water pressure from the well (65 psi is the optimum).

Why these systems? Because they use more than 10 filtration steps to remove all contaminants commonly found in wells and more: Sediment, pesticides, industrial solvents, microorganisms, colloids, volatile organic compounds, PCBs, tastes, odors, metals especially iron, hardness, hydrogen sulfide (rotten egg smell), etc.

And if you want you can add a UV treatment stage on top for 99.99% reduction of bacteria, viruses, and protozoa. This turns the Crystal Quest 1000C into the 3000C, and the 1000CP into the 3000CP.

Please note: According to Crystal Quest, the above systems can handle very hard water with up to 15 gpg hardness. Iron content shouldn’t exceed 2 ppm. This will result in a filtration capacity decrease of no more than 5%. At higher iron/hardness levels, the filters and membranes will clog prematurely. Tip: Contact Crystal Quest live support to discuss custom pretreatment.

Crystal Quest RO Under Sink Water Filter - 1000C

Crystal Quest RO Under Sink System – Model 1000C

System Price:$$
Filter Stages:12
Purified Water:Up to 50 GPD
System Certifications:

Our Rating

System Pros

  • Reverse osmosis under sink water filter systems use 12 stages of filtration.
    • Filter stage 1 is an activated carbon block (5-micron nominal). It adsorbs chlorine and all kinds of chemicals. Furthermore, it traps undissolved matter to protect the following filter stages from clogging.
    • Stage 2 is a 0.02-micron ultrafiltration membrane. Ultrafiltration is effective for the reduction of microorganisms and other organic and inorganic molecules.
    • At stage 4, the water passes through granular activated carbon (GAC). Say goodbye to 99.9% chlorine, bad taste and odor, and dozens or even hundreds of chemicals that may be lurking in your water.
    • Next comes an ion exchange resin. It filters metals – think lead – and water hardness.
    • Stage 6 + 7 is Eagle Redox Alloy filter media, a blend of copper and zinc. They combine electrochemical oxidation & reduction with adsorption. This takes care of hydrogen sulfide, iron, mercury, chromium, cadmium and other dissolved metals. The media also inhibits bacterial growth throughout the entire system.
    • The reverse osmosis membrane (stage 9) rejects all particles larger than 0.0001 micron.
    • And lastly, filter stage 11 is another GAC filter to remove any residual tastes.
    • Stages 3, 8, 10, and 12 are filter pads. Rated at 1 micron, they remove suspended particles like silt, sand, rust, sediment, and cyst.
  • Enough output water flow for family use.
  • Optional: Ultraviolet light filter. Kills 99.99% of bacteria, viruses, and protozoa.
  • Optional: Nitrate filter. Might be necessary if you live close to agricultural lands or animal feedlots.
  • Optional: Fluoride filter. For high organic fluoride in well water.
  • No more difficult to install than other under sink RO systems.
  • Maintenance requirements are kept at a bare minimum. Cost: $100-155 per year. You can subscribe to save 5%.
  • 1-year limited warranty.

System Cons

  • Installations directions are a bit vague.
  • No NSF tests.

4. Our #1 Portable RO System: Crystal Quest Thunder

The Crystal Quest Thunder is our number one portable reverse osmosis system this year. That’s because it can be attached to any standard faucet in a matter of seconds – at home, in your RV, or while you’re on the move. This plus the compact design make it the ideal travel companion.

Customer satisfaction is high and the price tag is reasonable. Our only issue is that we’re missing NSF testing/certifications with specific contaminant reduction rates. 4.5 stars!

Crystal Quest Thunder Reverse Osmosis System

Crystal Quest Thunder

System Price:$$
Filter Stages:10
Purified Water:~50 Gallons Per Day (GPD)
System Certifications:

Our Rating

System Pros

  • Don’t have much space? Measuring 16x7x7 inches, the Crystal Quest Thunder is one of the smallest and thus most portable RO water filtration systems we know.
  • 10-stage filtration process removes sediment, cyst, chlorine, VOCs, bad taste/odor, pesticides, metals, salts…
    • Granular activated carbon, RO membrane, copper-zinc redox alloy (KDF), and ion exchange resin are separated by 1-micron filter pads.
    • Bacteriostatic filter media inhibits fouling.
  • Filtered drinking water tastes very clean.
  • System is rated at .03 gallon per minute water flow which equals 2 gallons per hour.
    • Not super fast but fast enough when used in combination with a large container to store the purified water in.
    • Minimum required water pressure is 45 psi.
  • Tool-free installation is quick and easy – faucet adapters included.
  • Replacing filters is child’s play thanks to quick-connect fittings.
    • Replace granular activated carbon cartridge every 12-18 months, RO membrane and SMART filter every 2-3 years. Average annual cost: $65-100 which is cheap.
  • Crystal Quest customer service is great.
  • Unit is covered by a 1-year warranty.

System Cons

  • No NSF certifications.

→ Detailed Crystal Quest Thunder Review

5. Our #1 Tankless RO System: Waterdrop WD-G3-W Purifier

Delicious water, sleek design, straightforward under-sink install, and effortless filter changes – the Waterdrop WD-G3-W is our go-to tankless reverse osmosis system in 2021. No tank means the unit filters water on demand rather than storing it in a tank which saves quite a bit of space under your kitchen sink. Taking into account the high initial purchase price, it’s worth 4 stars from us.

Waterdrop WD-G3-W Under Sink Reverse Osmosis System

Waterdrop WD-G3-W Tankless Under Sink RO System

System Price:$$$$
Filter Stages:3
Purified Water:0.28 Gallons Per Minute
System Certifications:NSF 58

Our Rating

System Pros

  • Tankless design saves space.
  • 3-layer composite filter (polypropylene cotton + coconut shell activated carbon block) removes chlorine, bad tastes and smell, and sediment like sand and rust.
  • RO filter membrane rejects harmful metals, bacteria, viruses, and much more.
  • Another activated carbon block filter gives the water a finishing touch improving aesthetics.
  • System is NSF Standard 58 certified for 94% TDS rejection.
  • Built-in pressure pump increases water flow to 0.28 gallons per minute to eliminate long waiting times. One cup fills in little more than 10 seconds.
    • The pump also reduces the amount of wastewater flowing down the drain from the standard 3-5 gallons for every gallon of filtered water to as little as one gallon.
  • All plastic is BPA-free to avoid recontamination.
  • The dispenser is metal for high durability.
  • Waterdrop reverse osmosis systems can be installed by non-professionals within one to two hours.
    • You shouldn’t have problems if you’re handy with tools and as long as you follow the instructions provided.
  • Smart faucet uses LED to indicate filter status. Blue light means your filters are working just fine. When you see yellow light you have less than 40 gallons of filtered drinking water left (about 15 days). Change filters immediately once you see red light and hear beeping sound when dispensing water.
    • Similar lights are found on system front panel.
    • You no longer need to remember date of next filter change.
  • TDS monitor on system front panel also indicates filtration effectiveness which is another feature to oversee filter status.
  • Filter replacements can be done in 10 seconds with no need for tools and closing feed water line. Yearly cost: We estimate roughly $115.
  • Other important features: Auto-flushing to prevent fouling and leak protection.
  • Waterdrop WD-G3-W reverse osmosis water filtration system comes with a 30-day money-back guarantee that allows you to return the product for a full refund + manufacturer warranty (one year).

System Cons

  • High initial cost.
  • We have little doubt that the Waterdrop is effective but we would have preferred more lab testing.
  • Some people need to drain a full gallon of water before the system achieves optimum TDS.
    • Hardware or software error?

→ Full Waterdrop Reverse Osmosis Review

6. Best Cheap Reverse Osmosis System: NU Aqua Platinum Series – 5 Stage Water Purification, 100GPD

The NU Aqua Platinum Series 5-stage reverse osmosis system is perfect for people on a tight budget. It comes at a fraction of the cost of what you pay for the units of some of the leading brands. And not only that, you also get free shipping, a TDS meter, a 180-day satisfaction guarantee (refund or credit of original purchase amount if filtered water doesn’t meet your expectations), and a full 5-year warranty. On top of that, replacement filters for one year cost as little as $50 which is unheard of.

How can the Nu Aqua RO system be so cheap? According to the company, that’s because Nu Aqua is the manufacturer of their own products. There’re no middle men so they can offer the best possible prices. We like! 3.5 stars.

NU Aqua 5 Stage Reverse Osmosis System 100 GPD

NU Aqua Platinum Series 5 Stage 100GPD RO System

System Price:$
Filter Stages:5
Purified Water:100 GPD (Theoretical)
System Certifications:

Our Rating

System Pros

  • Five stages of filtration.
  • 1-micron polypropylene sediment filter rids incoming water of visible particulate matter: Dirt, sand, dust, rust, debris. Extends the life of the other filters in the system.
    • Clear filter housing allows for easy monitoring.
  • Granular carbon fiber removes chlorine, pesticides, color, bad taste, odor-causing compounds, and overall finer particles that the first filter stage may have missed.
  • Coconut carbon block filters chlorine, chloramine, heavy metals, VOCs, giardia, cryptosporidium.
  • The thin-film composite RO membrane rejects even the smallest dissolved solids: Salts, metals like lead, arsenic, fluoride, sulfate, radium…
  • Before the water comes out of the chrome dispenser it passes through an inline post-filter made of activated coconut shell carbon. It removes any last traces of flavor or odor to make sure you get the freshest possible taste.
  • High flow membrane (100 gallons of water per day) fills tank in less than 2 hours, perfect for large households with up to 6 people.
  • All parts are BPA-free to keep water as pure as possible.
  • Almost anyone can install this RO system in one afternoon. Step-by-step installation DVD and owner’s manual included.
  • Nu Aqua reverse osmosis systems are “a breeze to maintain”.
    • Replace filters every 6-9 months and RO membrane every 1-1.5 years.
    • Replacement sets are super cheap.
  • TDS meter as free bonus.
  • Backed by 180-day satisfaction guarantee and full 5-year warranty.

System Cons

  • Written installation directions could do with an upgrade.
  • Most parts are plastic.

7. Review: Home Master HydroPerfection (TMHP) Reverse Osmosis Drinking Water Filter System

The HydroPerfection, or TMHP, combines the best of all Home Master reverse osmosis systems such as a thorough water purification process including UV light treatment suited for both well and tap water, remineralization, and a built-in permeate pump which increases total daily water production while reducing wastewater. The result is an unlimited amount of highly purified and great-tasting alkaline drinking water. You just need to be willing to pay a premium. 4.5 stars!

Make sure to use our coupon code BOSFREERO at checkout and get FREE SHIPPING!

Home Master HydroPerfection TMHP Reverse Osmosis System

Home Master HydroPerfection (TMHP)

System Price:$$$$
Filter Stages:9
Purified Water:75 Gallons Per Day (GPD)
System Certifications:

Our Rating

System Pros

  • One of the few companies that produces their water systems in the U.S. (Arizona).
  • Uses 5-micron sediment pre-filter, 5-micron coconut shell catalytic carbon + KDF-85 pre-filter, DOW FILMTEC RO membrane, UV light filtration, and coconut shell GAC remineralization filter to trap sediment, remove cloudiness, taste, and odor, and reduce contaminants like arsenic, chromium-6, lead, radium, chlorine, chloramine, iron, hydrogen sulfide, and chemicals and organic contaminants including pesticides. Ultraviolet filter kills 99.99% of bacteria, viruses, and other microorganisms.
  • Mineral stage adds calcium and magnesium back into water (restores 30-60 ppm) for better taste and more alkaline water.
    • Also prevents storage tank degradation.
  • Non-electric permeate pump reduces water waste from the average four gallons wasted for every gallon of filtered water down to one.
  • Enough water for large families. Faster than normal output water flow let’s you fill a large pitcher in no time.
  • Easy and straightforward DIY installation. Quick-connect fittings, color-coded tubing, detailed instruction manual + 6-part video series, live support.
  • Modular filter elements can be replaced without tools (replace cartridge + entire housing).
    • Last a full 2,000 gallons or one year. Reverse osmosis membrane is good for 3 to 5 years. Cost: $150-160 which is okay taking into account the number of filtration stages.
    • Modular design prevents flooding and accumulation of germs.
  • Home Mater reverse osmosis systems are backed by 5-year limited warranty + 30-day satisfaction guarantee.

System Cons

  • High initial price tag.
  • A few people had difficulties with the install.
  • We would have liked testing against NSF standards.

→ Read Our Full Home Master HydroPerfection Reverse Osmosis Review Here

Reverse Osmosis Filters Comparison List

FiltersDesignNotes on Model
AquaTru RO SystemProcess with 4 Water Filters, Separate Water Storage TankUnit Filters Most Contaminants (According to Company Testing Results), Requires Electricity, Easy to Install & Maintain, Carbon Filtration
Aquasana OptimH2O Under Sink RO System4 Filters, Separate Water Storage Tank, Dedicated FaucetLower Water Pressure, Filters Most Contaminants (According to Manufacturer Testing Data), Makes Use of Catalytic Carbon, Remineralization Stage Adds Minerals Back to Clean Water (Raises pH), Regular Under Sink Install
Crystal Quest 1000C & 1000CP Reverse Osmosis Systems for Well Water5 (12) Water Filters, Separate Water Storage Tank, Dedicated FaucetFilters Hydrogen Sulfide, Regular Under Sink Installation
Crystal Quest Thunder Portable Reverse Osmosis Filtering System5 (10) Filters Process, No Tank, Dedicated FaucetEasy to Install
Waterdrop WD-G3-W Reverse Osmosis System without Tank3 Water Filters, No Water Tank, Dedicated FaucetMakes Use of Double Carbon Blocks, Booster Pump Boosts Increases Water Pressure & Filtered Water Efficiency (Less Waste Water), Easy Installation + Maintenance
NU Aqua Platinum Series 5 Stage 100 GPD RO System5 Water Filters, Separate Water Tank, Dedicated FaucetCheap, Straightforward Installation + Maintenance
Home Master TMHP HydroPerfection RO System9 Filter Stages, Separate Water Tank, Dedicated FaucetTFC RO Membrane, Makes Use of Catalytic Carbon, Remineralization Stage Adds Minerals Back to Clean Water (Raises pH), UV Filter Kills Bacteria & Viruses + Other Types of Microorganisms, Permeate Pump Boosts Water Pressure & Filtered Water Efficiency (Less Waste Water), Straightforward Installation + Maintenance

Other Reverse Osmosis Water Filter Reviews

Buying Guide: What You Need to Consider When Choosing an RO System for Your Home

What do you need to consider when searching for the best home reverse osmosis system?

Reverse Osmosis Systems and NSF Certifications

They may be more important with other water filtering solutions, but with RO systems, too, one should choose a unit that’s NSF certified (or tested) if possible. NSF certifications not only ensure that a reverse osmosis system actually performs as claimed by the manufacturer, but also that it’s made from high-quality materials.

  • NSF Standard 42 tests water filtration systems for the reduction of aesthetic non-health-related contaminants, most importantly chlorine. The scope of the standard also includes material safety and structural integrity.
  • Standard 53 tests systems for the reduction of contaminants with health effects regulated by the U.S. Environmental Protection Agency (EPA). These include cysts, some heavy metals, and volatile organic compounds (VOCs) among others. Again, the scope also covers material safety and structural integrity of a product.
  • Standard 401 tests filtration systems for the reduction of 15 different “emerging compounds“. These are pharmaceuticals and chemicals not yet regulated by the EPA.
  • NSF Standard 58 is for RO systems specifically. It establishes the minimum requirements for the reduction of a whole range of contaminants, such as TDS (Total Dissolved Solids), chromium 3 and 6, arsenic, nitrate/nitrite, and lead. Material safety and structural integrity are included.

Some reverse osmosis systems are also certified by the FDA which we consider less important.

The Water Filtration Process

Generally, top-notch RO systems feature at least 4 to 5 stages of filtration water has to pass through before it comes out of the dispenser:

  • 1. Sediment filters – Trap soil particles, rust, sand, dust…
  • 2. Carbon filters – Remove disinfectants, organics, chemicals, unpleasant odors and tastes, a few heavy metals, and even cysts if the micron rating is small enough.
  • 3. Granular carbon – Same as stage 2.
  • 4. Reverse osmosis membrane – The reverse osmosis membrane rejects more or less all remaining contaminants including salts, metals, bacteria, and viruses.
  • 5. Coconut shell post filters – Remove any residual taste.

Some pricier RO systems come with additional components, for example to remineralize the water and balance pH by adding bits of calcium and magnesium.

RO membrane

System Style

There are 3 types of reverse osmosis systems: Countertop, under sink, and whole house. You’re probably looking for option 1 or 2. Whole house reverse osmosis systems are seldom needed for home use.

Personally, we prefer countertop-style systems because they’re installation-free and thus portable. That said, installing an RO system under the kitchen sink is not that big of a deal either (more info below). Performance-wise, there’s no difference between the best products from either categories.

Water Demand

A product must be able to meet your water demand. This means you want a large enough storage tank or, if there is no storage tank, a high enough flow rate.

RO System Installation and Filter (Membrane) Replacements

Countertop RO systems are either autarchic or they connect to any standard kitchen faucet in under 5 minutes. It doesn’t get any easier than that.

In contrast, even well-designed under counter reverse osmosis systems require proper installation which includes a few intrusive changes. Most importantly, you need to drill a hole in your kitchen countertop or sink (unless there’s a spare one) to accommodate the RO faucet. And you have to establish a drain connection which involves drilling in the sink’s drain line.

As for filter/membrane replacements, RO water systems featuring a modular design are the preferred choice here. Whenever you replace one of the filter elements you dispose the entire housing. This prevents bacteria and other germs from accumulating, plus the whole process doesn’t take more than a few minutes. No need to turn off the water supply, no spilling, no worries. The only drawback: Modular filters can be more costly than those with separate housings.

Feed Water Pressure and Water Wastage

All reverse osmosis systems waste water. That’s just how the process works. However, the issue becomes worse if you’re homes feed water pressure is below the optimum. Fortunately, there’re electric pressure pumps and permeate pumps to reduce water wastage significantly. Some RO systems already have them built-in, like the AquaTru. Others can be upgraded.


We get it, people’s budget is rarely unlimited. Still, don’t make the mistake and buy a reverse osmosis system that’s low-quality. Those things can be a source of trouble – think leaking. Furthermore, cheap materials might leach new contaminants into your water that weren’t there in the first place.

You should also pay attention to cost and availability of replacement filters/membranes.

Where to Buy

In our opinion, the best place to buy a reverse osmosis system is online. You not only have the largest product selection possible, you also get the best prices. Above that, with point-of-use RO systems there’s usually no need to consult a local water expert.

More on Reverse Osmosis Systems

In the first section, we reviewed the best RO systems currently available on the market. Then we talked about what to look for in a proper unit. Lastly, we’ll answer some common reader questions.

What is Reverse Osmosis?

Reverse osmosis is one of the safest water filtration methods which many U.S bottlers rely on. But what exactly is reverse osmosis and how does it work?

We like to explain reverse osmosis by first explaining the natural osmosis process:

In chemistry class, you may have learned that if two salt solutions are separated by a semipermeable membrane the solvent always moves from the low to the high concentrated side due to what’s called “osmotic pressure”. The process continues until both salt concentrations on either side of the membrane are equal.

In reverse osmosis the exact opposite happens. External hydraulic pressure (your home’s feed water pressure) is used to overcome the osmotic pressure and the flow of the solvent, usually water, is reversed. Now the water molecules move from the high concentrate solution (feed water) to the low concentrate solution (drinking water). The aim is to separate the solvent from the dissolved impurities resulting in purified water.

Bottom line: Reverse osmosis is a method of filtering water which allows it to leave almost all impurities behind so that you end up with pure H2O.
Reverse Osmosis Process Diagram

How Does a Reverse Osmosis System Work?

Based on the previous section you might be thinking a reverse osmosis water filtration system is composed of an RO membrane, a water storage tank, a faucet, and some tubing. In reality, it’s a bit more complicated…

The Different RO System Components and the X-Stage Filtration Process


We don’t know of any reverse osmosis water filter system that doesn’t feature at least one pre-filter stage. Pre-filters are used to protect the delicate RO membrane from fouling. Usually, they’re sediment or carbon filters or a combination of the two.

As the name suggests, a sediment filter removes sediments from water; sand, silt, and other large particles.

Carbon filters contain either granular carbon or a carbon block. We can also differentiate between activated carbon and catalytic carbon. The latter is more effective at removing a broader range of contaminants including chloramine. Generally speaking, carbon is good for adsorbing disinfectants and their byproducts, organic contaminants, and various chemicals.

RO Membrane

At stage 2 or 3, the semipermeable reverse osmosis membrane comes into play. It more or less rejects all remaining water contaminants including heavy metals, salts, fluoride, radiation, BPA, and microorganisms.

The purified water leaves the membrane to continue its journey through the RO system. A second water stream that carries the concentrated contaminants is flushed down the drain.


Following the RO membrane come one or more post-filters. This is usually another granular activated carbon filter which removes any residual taste and odor.

Storage Tank

Most reverse osmosis systems feature a water storage tank because they’re too slow to produce water on demand. The tank contains a pressurized water bladder to ensure fast flow when you open the RO faucet.

Automatic Shut-Off Valve

As the water storage tank fills it exerts increasing backpressure. Once the backpressure reaches about two-third of the incoming water pressure a piston in the so-called automatic shut-off valve (ASO) closes, preventing more water from entering the RO system. Only when water is dispensed by opening the RO faucet causing the storage tank backpressure to drop does the ASO re-open to allow new water to flow into the unit.


There are two types of faucets: Standard and air-gap faucets. An air-gap faucet features and air gap which acts as a siphon break to prevent drain water from flowing backward into the RO unit causing damage. Also, if the drain line is stopped up, the drain water can leave through the air gap.

RO systems that come with a regular non air-gap faucet usually feature one or more check valves to guard against drain backflow.

Check Valve

A check valve is a one-way valve. It allows reject water to flow to the drain but prevents it from flowing backwards toward the RO membrane in case of a blocked drain pipe.

Flow Restrictor

A flow restrictor creates pressure in the RO membrane to control the permeate-to-reject flow ratio. In other words, it controls how much water flows down the drain and must be matched to the capacity of the RO membrane.
reverse osmosis system installation diagram

Optional Components


RO water lacks minerals and thus tends to be slightly acidic. You can counter this by adding a remineralization stage. It balances water pH and the minerals will add to your daily nutritional intake.

UV Light

An optional UV light stage is great if you’re dealing with microorganisms. They UV light will render them harmless.

Permeate Pump

A non-electric permeate pump improves the permeate-to-reject water ratio so that less wastewater goes down the drain.

Electric Pressure Pump

Electric pressure pumps also lower the amount of wastewater while boosting overall water production.

About Reverse Osmosis System Water Efficiency Ratios

As mentioned before, no matter how well-designed and efficient a reverse osmosis system is, based on the nature of the RO process it will always produce some wastewater. The wastewater contains all the impurities rejected by the RO membrane and is usually flushed directly down the drain. In rare cases, usually with whole house reverse osmosis systems, the reject water is fed back into the water supply for recycling.

The ratio of drinking water to wastewater is a function of RO membrane pore size, solute concentration, feed water temperature, and feed water pressure. Larger pores, lower solute concentration, and higher water temp and pressure result in higher water efficiency.

However, you cannot or shouldn’t mess with the first three parameters. But what you very well can do is use a pump to increase low water pressure. 60 psi are considered ideal for most point-of-use RO units. Anything below 30 psi is generally considered insufficient.

How much water does a standard reverse osmosis water filtration system waste? Around 3 to 5 gallons for every gallon of purified water. In comparison, systems with an electric pump like the AquaTru waste no more than 0.25 per 1 gallon filtered. Systems featuring a non-electric permeate pump can achieve a 1:1 ratio at least.

What Do Reverse Osmosis Filtration Systems Remove from Water?

Listing every single water contaminant that a reverse osmosis system can possibly remove would take far too long. Instead, we decided to provide you with a list of contaminant groups:

  • Sediment
  • Water disinfectants (e.g. chlorine, chloramine)
  • Disinfection byproducts (e.g. TTHMs)
  • Volatile organic compounds
  • Nitrite/nitrates
  • Pesticides
  • Herbicides
  • Heavy Metals (e.g. lead)
  • Metalloids (e.g. arsenic)
  • Transition metals (e.g. chromium 6)
  • Salts & minerals
  • PFAS
  • Emerging chemicals/pharmaceuticals (e.g. BPA)
  • Microorganisms (bacteria, viruses, cyst)
  • Overall TDS


What Does TDS Mean?

TDS stands for Total dissolved solids and measures the combined total of dissolved organic and inorganic substances in water. The unit for TDS concentration is parts per million (ppm) and can be determined with the help of a TDS meter.

Is a Reverse Osmosis System Worth It? – Pros & Cons

Is a reverse osmosis system worth it? That’s a good question. In our opinion it is if you’re dealing with contamination that regular filtration alone cannot solve. What we mean by that is more stubborn contaminants such as chromium 6 or arsenic – both very harmful when consumed – that can only be removed by ion exchange or, well, reverse osmosis.

Apart from the health aspect, an RO system will also greatly improve the taste and smell of your drinking water (although some people describe the taste as “rather flat”).

Another pro is ease of installation and maintenance, especially with countertop units. Speaking of maintenance, although usually a tad more expensive to purchase when compared to regular water filters, most reverse osmosis filter systems are pretty cost-effective in the long run. And filtering your own tap water is certainly much, much cheaper than buying bottled water.

A last benefit that comes to mind is clear ice cubes. Yep, RO water is so pure that even when frozen it’s crystal clear.

As far as disadvantages are concerned, we have the fact that reverse osmosis always produces some wastewater, the permeate water is free from all impurities including healthy minerals, and the systems are relatively pricey at purchase.

Reverse Osmosis Water: Risks

Drinking water treatment by means of reverse osmosis filtration removes almost all impurities which is great. Only distillation can compete with the technology in terms of achieved water purity. But there’s one downside: An RO filter system cannot differentiate between healthy and harmful substances. As a result, it also removes essential minerals from water which in turn affects pH.

Let’s take calcium as an example: About 20% of our recommended daily intake (RDI) comes from the water we drink. The remaining 80% comes from our food. So if we drink RO purified water instead of bottled water chances are that we may not cover our calcium RDI entirely. The same applies to magnesium. For all other minerals, including iodine, iron and zinc, drinking water provides less than 5% of the RDI.

Water that has been deprived of its mineral content also tends to be slightly acidic which, according to our research, shouldn’t pose a problem. It might be more corrosive but that doesn’t make a difference when stored in an RO tank or consumed directly.

How to Remineralize RO Water

You’re concerned about using RO water for drinking and cooking and therefore not meeting your daily demand for essential minerals? The most convenient solution is to add a remineralization stage to your reverse osmosis filtration system. During the additional treatment step, beneficial minerals like calcium, magnesium, and potassium are released into the water. It doesn’t get any easier!

Another option is to use an electrolyte blend. The main focus here should be a balanced mineral composition. About 60 ppm calcium and 25 ppm of magnesium are ideal. An alternative to electrolyte blends are green powder blends and mineral-rich salts, e.g. Himalayan salt.

Do You Need a Reverse Osmosis System?

There’s only one way to answer this question: Identifying the type(s) of water contamination you’re dealing with. You can do this by checking your water quality report. If you’re on well water and don’t have access to an annual quality report, you can send a direct sample to a professional test lab in your area or do the testing yourself.

Each option has its own pros and cons. A water quality report has to be provided for free but utilities are only required to test for certain contaminants and contamination that happens while the water travels from the utility to your home cannot be detected.

Hiring a professional lab can get really expensive if you want thorough testing.

And doing your own testing at best can only give you a very rough idea of what you’re facing.

The Best RO Water System for Well Water?

If you live in a rural area and receive your water from a private well you’re probably be looking for a reverse osmosis system that works on wells – makes sense.

We usually like to recommend the Crystal Quest 1000C or 1000CP (see above). However, in some cases no matter how good an RO system, additional pre-treatment of the well water is required. Otherwise the different filter components and the delicate RO membrane in particular will clog in no time, as the water is simply too heavily laden with hardness minerals, sediment, or iron for example.

This pre-treatment could be a simple sediment filter setup with 3 cartridges rated at 50, 10, and 5 microns to remove dirt, rust, sand, silt, etc. For very hard water, you should consider installing a water softener in your home. With iron contamination, a different type of pre-treatment is required, depending on the iron type and concentration.

By the way, filtering raw well water with reverse osmosis alone is not a good idea. It could be biologically unsafe and therefore require some sort of disinfection such as shock chlorination. But this goes beyond the scope of this article. For now, all you need to remember is that well water oftentimes requires a different and more sophisticated approach than municipal water when it comes to the right treatment method(s). What should be your next step? Having your water tested.

How to Install a Reverse Osmosis System


Under-the-sink installation on the cold water line is the standard, obviously. If space is limited, consider your basement, garage, or a utility room and run a water line to the kitchen sink.

What you need to avoid is freezing temperatures. And always install a reverse osmosis system downstream of any other water treatment equipment.

Tools & Supplies

Do yourself a favor and gather all the necessary tools and supplies before you start with the actual installation:

  • Power drill
  • ¼” (⅜”) (½”) drill bit (size depends on faucet type used)
  • Screwdriver
  • Tubing cutter
  • Utility knife
  • Adjustable wrench
  • Towel
  • Bucket

Installation Process – Step by Step Instructions

Equipped with the right tools and detailed instructions, a reverse osmosis system DIY installation shouldn’t be too difficult to pull off for most people. Plus, you can find plenty of helpful tutorials on YouTube.

The following is a general description of the installation process. Please keep in mind that individual steps may vary from system to system and your specific plumbing setup.

1. Faucet

First of all, drill a hole for the new RO faucet. It should be positioned with convenience in mind.

Mark the spot with a center punch. Then drill the hole. Go extra slow when you are about to hit any metal. For a ⅜” or ½” hole, drill a smaller pilot hole first. Clean up any sharp edges before inserting the faucet stem through the hole and securing it from the bottom. Attach the quick-connect fitting.

2. Drain Saddle

For the drain saddle or adapter, you need to drill into your sink drain line. Go above and as far away as possible from the dishwasher discharge and garbage disposal, and at least 6″ above the p-trap.

Drill a ¼” hole in the top or the side of the drain line. Attach the drain clamps with screws. Be careful not to overtighten.

3. Feed Valve

The feed valve connects your reverse osmosis system to the cold water line.

Start by closing the cold water supply. Open your regular kitchen faucet to release any pressure and remove the tubing from the cold water valve over a bucket. Install the new feed valve and close it for now. Connect the cold water tubing to the new valve and turn the water back on.

4. Storage Tank

Place the water storage tank within 10 feet of the dispenser. Wrap enough Teflon tape around the threaded port at the top. Screw on the tank valve/connector.

5. Set Up RO Module

You can mount the RO module if you want. When done, establish each connection using the color-coded tubing. Most reverse osmosis system feature quick-connect fittings. Simply push in the tubing as far as it goes. Pull back gently to check each connection.

6. Filter Elements

Install the different filtration elements including the reverse osmosis membrane as instructed in the manual.

  • For regular filters, remove housing, insert cartridge, screw housing back, and carefully tighten with wrench.
  • For RO membrane, remove housing cap, push membrane into socket, and put housing cap back on.

7. Finishing the Installation

Almost done! Now it’s time to open the feed water valve and the dispenser to check for leaks.

It may take 10-15 minutes for the water to start dribbling out of the dispenser. Close the RO faucet and open the storage tank valve. Wait for the tank to fill completely. As soon as you can’t hear any more water running down the drain, drain the entire tank. Repeat the process and flush a second time.

Reverse Osmosis Water Filter System Maintenance

RO maintenance
Regular filter replacements are critical when it comes to reverse osmosis water system maintenance. Most filters require changing every 12 months. An RO membrane can be good for up to 3-5 years.

We also recommend annual system cleaning/sanitizing and making sure storage tank pressure is correct.

Filter Changes

Sediment or carbon, all filters need to be replaced sooner or later. How often? It depends on the filter itself as well as feed water condition and your water consumption. Our tip: Check the manufacturer recommendations.

How to replace? In a nutshell:

  1. Close the incoming water and storage tank valves.
  2. Depressurize.
  3. Remove filter housings.
  4. Insert new filter cartridges.
  5. Screw housings back on.
  6. Open valves.
  7. Flush new filters while checking for leaks.

Membrane Replacement

Most RO membranes last around 3 years. For a more scientific approach, you can test the remaining effectiveness of your membrane with the help of a TDS meter. How? Measure feed water and permeate water TDS. Then use this formula to calculate your current TDS rejection rate:

Rejection rate in % = (Total Dissolved Solids of untreated tap water – Total Dissolved Solids of pure water) / Total Dissolved Solids of untreated tap water x 100

If the rejection rate of your current membrane is below 80% it’s time for a new one.

Side note: A membrane in perfect condition removes up to 99% TDS.

System Cleaning

Although not necessary in all cases, ideally you want to clean (and sanitize) your reverse osmosis water filtration system once a year.

  1. Start by removing all filter elements.
  2. Scrub the inside of each filter housing with warm dishwater and rinse afterwards.
  3. Optional: For sanitizing, add unscented household bleach into the housing of filter stage one. Then screw all other empty filter housings back on. Allow the storage tank to fill and let the bleach to stay in the system for at least 30 minutes. Flush the entire tank. Let the tank refill a second time and flush out. While you wait: Soak the RO membrane in the right chemical solutions as recommended by the manufacturer to prevent fouling and scaling.
  4. Reinstall all filter elements.

Frequently Asked Questions

  • How long does a reverse osmosis system last?
    As long as you want it to, provided that you take good care of it.
  • Is reverse osmosis worth the money?
    Absolutely, if you want high-quality water.
  • What is the pH of reverse osmosis water?
    The pH of most RO waters is slightly acidic. That’s because it lacks minerals like calcium and magnesium. We suggest remineralization before use which will raise the pH.
  • How much does it cost to install a reverse osmosis system?
    Portable systems are installation-free so it costs nothing. As for under sink models, prices start at $150. You can also do this yourself if you’re not afraid to drill a hole in your kitchen counter and drain pipe. If you decide to hire a plumber make sure to reach out to more than one company so that you can compare estimates.
  • Does an RO system work better if it costs more?
    Not necessarily. There’re great systems that are still affordable. However, from our experience you can’t expect good quality below a certain budget.
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Questions about reverse osmosis systems? Ask Away!

And make sure to revisit this buying guide from time to time as we are going to continue our hunt for the best reverse osmosis system and add new reverse osmosis system reviews occasionally.

About the Author Gene Fitzgerald

Gene Fitzgerald has been with BOS since the very beginning. She is head of content creation and has fully immersed herself into the home water treatment industry only to become an expert herself. Outside of BOS, Gene loves reading books on philosophy & social issues, making music, and hiking.
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