Is There a Gravity-Based Reverse Osmosis Water Purifier?
Written by: Alexandra Uta // Last Updated: Mar 27, 2023
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Gravity-based water filtration is quite popular among people who want to have a consistent supply of fresh water without having to depend on electricity or water pressure from a plumbing system.
At the same time, reverse osmosis is renowned for its advanced water purification capabilities and thorough operation.
For some people, this leads to the obvious question – is there a device that combines both gravity filtration and reverse osmosis? Like a gravity reverse osmosis water filter?
It’s not feasible to integrate reverse osmosis in a gravity water filter.
Doing so would require a “water tower” more than 130 ft in height.
Is There a Gravity-Based Reverse Osmosis Water Purifier?
Unfortunately, there’s no such thing as a reverse osmosis gravity filter on the market.
It doesn’t make sense physically, because reverse osmosis requires high water pressure to work. A gravity-based water filter could theoretically provide that pressure, but in practice, it’s pretty much an unattainable goal.
Don’t believe us? Consider this: A reverse osmosis system requires around 60 psi of feed water pressure for optimal operation, which equates to 60 pounds of pressure per square inch.
Now, 60 pounds of water is equivalent to around 7.2 gallons, which is how much you’d need to store for every square inch of your gravity reverse osmosis water filter. To store that much water over just one square inch, you’ll need a tower that’s more than 1,660 inches in height – or over 138 feet!
Here’s a breakdown of the math in case you are interested:
2 gallons of water = 1663.2 cubic inch
2 inch3 / 1 inch² = 1663.2 inch = 138.6 feet so ridiculous height
What Is a Gravity Water Filter and How Does It Work?
A gravity water filter uses gravity to pull water between two containers. Water is poured into the top container, from where it naturally makes its way to the bottom one, passing through a single stage or a set of filters along the way. This purifies the water without requiring any additional power or pressure.
Gravity water filters can use a variety of filtration elements to purify the water that passes through them. Some are relatively simple, using a charcoal filter and not much else. Ceramic filter candles are very popular in these devices, and can also be purchased separately for a DIY approach if you want to create your own filter.
Aside from that, gravity-fed filters are available in two main variants – countertop and bag. The former is designed to be used indoors without moving it around much, while the latter is perfect for outdoor use, like camping trips.
What Is a Reverse Osmosis System and How Does It Work?
On the other hand, a reverse osmosis system uses a very fine, semipermeable membrane, forcing water through it at high pressure. The membrane is fine enough that only water molecules can pass through it (with some minor exceptions), which is where the purification strength of the process comes from. However, for this to work, you need a lot of pressure as we explained above.
This provides one of the most thorough modes of water purification available on the market right now. For this reason, reverse osmosis systems are very popular not just on the consumer market, but also in the industrial sector. Reverse osmosis is the default purification method used in many advanced water facilities.
One disadvantage to reverse osmosis is that it tends to waste a lot of water. Normally, more than 50% of the input water will go to waste. This can be improved first and foremost by adding pressure pumps.
Pros and Cons of Gravity-Based Water Filtration
Pros
Always have access to fresh, purified water, regardless of your circumstances. Never find yourself in a situation where you’re out of fresh drinking water because the power went out.
Low cost. Gravity-based water filters are among the cheapest options for water filtration on the market.
Easy to install and maintain. You don’t need to be experienced with tools to install a gravity water filter, and its maintenance is pretty simple too.
Can be used on the go (if you buy an appropriate model). Buying a gravity water filter bag means that you can filter your water on the go, for example when you’re on a camping trip.
Cons
Takes time to work. You must give the filter some time to work and, aside from filling the feed water container all the way to the top, there’s no smart hack to force it to operate faster.
Must refill the filter manually. You have to pay attention to the water level of the filter and refill it when it’s running low.
Doesn’t filter as thoroughly as reverse osmosis. If you’re looking for water filtration that’s as thorough as possible, reverse osmosis is a better option.
Most thorough method of water purification available. Reverse osmosis removes pretty much all contaminants you might be interested in, and it does so with a high level of efficiency.
Can run for a long time without any maintenance. These systems don’t require a lot of maintenance, and the necessary procedures don’t take a lot of effort.
You can store fresh water in a large tank. It’s easier to use a large storage tank with a reverse osmosis system compared to a gravity-based one.
Cons
More expensive. Due to their advanced construction, reverse osmosis filters can cost significantly more than gravity-based ones.
Not portable. There’s no way to make a portable reverse osmosis system. While compact dispenser-type models do exist, those are usually not suitable for camping trips or other types of outdoor use.
Can’t construct one yourself. The construction of a reverse osmosis system goes way beyond the scope of a regular DIY project.
Wastes water. You’ll waste some water in the filtration process, and the amounts can be significant if you don’t use additional measures.
If you have any questions about “gravity-based RO water purifiers” please don’t hesitate to leave a comment below!
About the Author Alexandra Uta
Alex is a content writer with an affinity for research and a methodical attention to detail. Since 2020, she has fully immersed herself into the home water treatment industry only to become an expert herself. Alex has been using water filters and similar products for years which has gained her lots of hands-on experience.
Learn more about Alex and the rest of the BOS Team.
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Leave a Comment:
Roger Stotts says
May 21, 2023
I purchased from Amazon a Purewell 3-Stage 0.01μm Ultra-Filtration Gravity Water Filter System, NSF/ANSI 372 Certification, 304 Stainless Steel Countertop System with 2 Filters and Stand, Reduce 99% Chlorine, 2.25G, PW-OB My plan is to use water from a dehumidifier and process it through the gravity filter to purify it. ANY COMMENT ON THIS IDEA?
Hi Roger,
Can’t really comment on that; onyl this: Stagnant condensate may harbor biological contaminants – think mold and mildew – particularly if the container isn’t cleaned regularly. And the condensate may contain metals like lead as residues from the dehumidifier components.
The Purewell may or may not remove all of these, but personally, I wouldn’t put myself at risk.
