How to Make a DIY Under Sink Water Filter

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The idea to build an under sink water filter from scratch seems far-fetched, doesn’t it? After all, a good under sink system is nifty, compact, neat, and doesn’t fall apart too soon.

Contrary to popular belief, you can build an inexpensive under sink water filter yourself, provided you have prior knowledge of plumbing and different types of filter cartridges at hand. But is it worth it, and will it be as good as a store-bought filtration system?

Stay with us as we answer these questions and take you through a step-by-step guide for building a DIY under sink water filter.

Key Takeaways

Here is how to make your own DIY under sink water filter:

  1. Gather the necessary tools and supplies (see list)
  2. Have your water tested to know what type of filter(s) you should use.
  3. Use standard-sized filter housings in sequence and arm them with filter cartridges. Tip: Choose filter cartridges that have undergone NSF testing.
  4. Connect the various filter stages to one another.
  5. Mount the filter unit near the cold water line underneath your kitchen sink.
  6. Connect the system to the cold water line using a feed water adapter.
  7. Connect the outgoing water supply to the sink faucet.

Is It Worth It?

A water filter is not just an investment in your home. It’s also an investment in your health and safety. It’s like a bit of a sidekick that helps you tackle the most crucial part of your diet: water.

Naturally, you are inclined to make wise decisions, and only you are the best judge of your abilities. So if you have a knack for DIY, want to save money, or just fancy a plumbing project, go ahead!

But remember, it is not like your homemade water filter science project, including a plastic bottle and some sand. We are talking about some heavy-duty plumbing; that’s no joke.

Besides, top brands like Clearly Filtered, Aquasana, and Pelican go through years of research and development to design their advanced water filtration systems. Then, they make sure to comply with NSF standards to ensure the filtration is efficient.

Maybe your homemade under sink water filter will do an excellent job, or perhaps, it will do just nothing. Unfortunately, there’s no easy way to tell.

Moreover, it entails quite a lot of work, tools, supplies, and components. As a result, you might end up spending more than the cost of a high-quality branded under sink filter. So, before you run to the hardware store, pause and think if your effort will be worth it.

How to Make Your Own DIY Under Sink Water Filter

You’ve made your decision and want to jump in? Let’s get started.

Test Your Water

To start, you have to decide what you want to filter out of your water. Since no one under sink water filter will get rid of all contaminants, you must have a fair idea about what you are attempting to remove.

Therefore, testing your water is the first and most important step whether you want to purchase an under sink filtration system or DIY it.

Water Testing Report

Since most contaminants are invisible to the naked eye, you must get your water tested from a reliable certified laboratory.

Having your water tested at a government lab will cost you a nominal amount, whereas at a private lab it can cost anywhere ranging from $50-$500. The testing laboratory might also suggest the ideal filtration method for your specific problem.

You can also use a simple home water testing kit, costing approx $20. Alternatively, get an online annual water report for your area from

Gather Tools and Supplies

Here is a list of all the tools and supplies you will need.

  • Empty filter housings
  • Filter cartridges (discussed below)
  • Mounting panel (optional)
  • Water filter ¼-inch tubing
  • Water filter connectors
  • Water filter diverter valve
  • Feed water valve
  • Plumber’s tape
  • Filter housing wrench
  • Extra O-rings
  • Screwdrivers and basic wrenches

Filter Sumps

Our approach for making our own under sink water filter is as follows:

We use one or more standard-sized filter sumps in sequence and arm them with the 10-inch filter cartridges of our choice, based on the results we got from our water testing.

Of course, you can also use a module that combines two or three stages in a fixed build.

Going this route, you are free to switch between different types of under sink water filters to find out which works best for you. And using the 10-inch industry standard gives you the largest filter selection to choose from.

Selecting Filter Cartridges

Your own DIY under sink water filtration system is only as efficient as the filter cartridges you will use. So, we advise only buying the best you can and looking for NSF certifications to ensure they work as advertised. Here are the most common filter media or rather filter types for under sink systems available in the market.

Sediment Filters

A sediment filter is a mechanical filter that removes sand, dust, flecks of rust, silt, and other dirt from your water. Think of it like a sieve, with really tiny pores that prevent sediment from passing through.

These filters are best used as the first step in a multi-stage under sink water filtration system as they prevent sediment from entering and clogging subsequent filters. However, if your problem is only limited to turbidity, you can use one as a standalone filter.

Sediment filters are rated in microns which refers to their pore size. A variety of sediment filters are available in several micron ratings – down to the submicron level. Filters with a higher micron rating (bigger pores) like 25 will remove dirt and silt particles. In contrast, a 1-micron sediment filter will also remove cryptosporidium.

Different Water Filter Cartridges and Membranes

Granular Activated Carbon or Block Carbon

A carbon-based filter is excellent for removing chlorine, organic compounds, and pesticides from your water. This filter type, sometimes also called charcoal filter, integrates the techniques of adsorption and filtration, so the resulting water is free from nasty odor-causing chemicals, unpleasant tastes, plus some harmful pollutants.

The only difference between granular activated carbon and block carbons is that the former is fine loose carbon held together. In contrast, block carbon is formed by compressing powdered carbon together through heat and pressure (and a binding agent).

These under sink water filters are not very effective at removing dissolved inorganic substances, chloramines, and some other stuff.

KDF Filter Media

KDF filter media features high-quality copper-zinc alloy that eliminates chlorine, metals like iron and lead, hydrogen sulfide, and more. Besides, bacteria and other pathogens are stopped from accumulating in the filter system.

However, due to the limitations of these filters, they are usually used in conjunction with other filter types in a multi-stage purification system.

Iron Filters

If your water supply is high in iron, it is wise to add an iron filtration cartridge to the system. Most iron filters are designed to effectively remove iron, manganese, and hydrogen sulfide from water (commonly found together).

Hence, they mainly tackle rust and odor problems. Keep in mind some filters remove only ferrous iron and not dissolved ferric iron. Therefore, if you have identified a very high iron level, you must look for a filter that eliminates both types.

Ceramic Filters

Ceramic under sink water filters contain natural media that traps even the tiniest particles as water passes through them. Thanks to ceramic’s small pore size, these filters are excellent at removing protozoa and microbial cysts.

Unfortunately, ceramic is unable to remove any dissolved substances like chemicals or heavy metals.

Other Types of Under Sink Water Filters

The above filter types are just examples.

Depending on the kind of contamination you are facing, you may need to include other types of water filtration in your DIY under sink water filter – think catalytic carbon for chloramine removal or ion exchange resin if you really want to focus on certain heavy metals.

Assembling the Unit

Now that you have all the supplies on hand, it’s time to assemble the unit. First, wrap plumber’s tape around the quick connect adapters and insert them on the system’s ‘in’ and ‘out’ ports.

Then, mount the unit near the cold water line underneath your kitchen sink.

Connect the filter to the cold water line using a feed adapter. And connect the outgoing water supply to the faucet using the desired length of tubing. We advise using quick connect fittings for a convenient tool-free installation process.

If you have any questions about a DIY under sink water filter please don’t hesitate to leave a comment below!

About the Author Gene Fitzgerald

Gene Fitzgerald is one of the founders of BOS and currently head of content creation. She has 8+ years of experience as a water treatment specialist under her belt making her our senior scientist. Outside of BOS, Gene loves reading books on philosophy & social issues, making music, and hiking.
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