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Home » Water Education & Testing » How to Make a DIY Under Sink Water Filter

How to Make a DIY Under Sink Water Filter

By: Craig Smith
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How To Make A DIY Under Sink Water Filter

While a good quality under-sink water filter is reliable and reasonably priced, you might be considering a DIY filter. If you’re itching for a plumbing adventure to show off your mad skills, you can probably handle it. 

It is worth it, though? 

While you can build an inexpensive under-sink filter yourself, you can buy a pre-built filter for a decent price and it would be backed by a warranty. On the other hand, you can take pride in building something useful yourself, and who doesn’t like to save money?

We’ll discuss the steps involved in building an under-sink water filter yourself, and we’ll discuss whether it is something you should consider. Keep reading!

How to Make a DIY Under-Sink Water Filter

This is a basic step by step guide for making your own under-sink water filter, but your steps may vary based on your design.

Test Your Water

One of the most important steps in this process is deciding exactly what you plan to filter out of your water supply. No filter can remove everything, so you must choose what to target for removal. The first step in doing that is to test your water supply to find out what is in it. 

You can get a home test kit online here.


Home kits like this usually test for lead, mercury, bacteria, and many other harmful contaminants. With a kit like this, you can test before adding your filter and after. This would help verify how well your new under-sink water filter is working.

Alternatively, you can find out what is in your tap water by checking with your water treatment plant. Water treatment plants must make that available by law. You can also get an EPA water quality report for many cities. 

Neither of these options can give the complete picture, though, because the water travels through a lot of pipes on the way to your house and in your own plumbing system. The water could pick up a lot of contaminants during that time, so it is best to test it at your faucet.

If you want the most reliable and complete results then you may want to have your water tested by a lab. There are government ran and private labs, and you can expect to pay $25-500. Keep in mind that you’ll need to send your water for testing both before you add the filter and then again afterward if you want to be sure it is working properly, which means paying twice.

Gather the Necessary Tools and Supplies

You’ll need a few tools and supplies to construct your DIY under-sink water filter. These may not be all the tools and all the supplies you’ll need, but these are the basics.

  • Screwdrivers and wrenches
  • Teflon tape
  • Tubing
  • Bypass valve
  • Water filter sumps
  • Filter cartridges
  • Water filter wrench
  • Connectors
  • O-rings

Depending on your design and installation location, you may need more or different supplies. 

Filter Sumps

You’ll need at least one filter sump. These are the housings that hold the filter cartridges, like this one from Pentair:


If you are planning to use multiple filter types, you’ll need a sump for each. We’ll talk more about the filter cartridge types below.

It’s best to go with industry standard sized filter sumps of 10” when buying your sumps. That lets you buy typical filter cartridges, and you can get cartridges to filter whatever you need to remove from your drinking water.

Filter Cartridges

You’ll need a filter cartridge for each sump. This is the actual filter inside the unit, and should look similar to this one from Membrane Solutions:


You can select from many common filter types, since different cartridges filter out different contaminants. Check your water test results to decide which water filter cartridges you want. Always look for NSF-certified filters so you can trust that they will perform as advertised.

Sediment Filters

Sediment filters are the most basic filter cartridge type. They remove things like rust particles, sand, and dirt from the water. If you go with a multi-stage setup, this should be the first filter in the line.

You’ll usually see sediment filters rated in microns. This is the pore size of the filter media, and this is how small something has to be to get through the filter. A larger number doesn’t filter as well, in this case. Sediment filters typically range from 1-50 microns. A 50-micron filter will filter only large particles, while a 1-micron filter can filter even microscopic parasites and bacteria.

Carbon Filters

Carbon filter cartridges are great at removing organic compounds, such as chlorine, VOCs, and pesticides. You may see these cartridges listed as activated carbon, granular activated carbon, carbon block, or charcoal filter cartridges. 

Carbon filters remove a lot of the odor-causing compounds and often improve the taste of the water. They aren’t there to remove suspended solids, just the organic components. While it’s good to include a carbon filter in your system to improve the odor and taste of your water, it usually isn’t the only filter.

Iron Filters

Iron filters are designed to remove iron, and usually do a good job of manganese and hydrogen sulfide. Excess iron in your water can be detrimental, but usually more worse for your sink, pipes, and drains than it is for your health. You’ll most likely see signs of this show up as reddish-brown stains around your drains, but it can also damage faucets and pipes. That’s why iron filters are a good idea in an under-sink water filter system.

KDF Filter Media

KDF filter media are made up of high-purity copper-zinc granules. These filters reduce contaminants in your drinking water through an oxidation reaction. They are good at removing heavy metals, chlorine, and bacteria. A KDF filter is typically used alongside other water filters, not alone.

Ceramic Filters

Ceramic water filters are made up of natural media with a very small pore size. They are great for removing bacteria, sediment, and microbes. A ceramic filter may have pores that are only a half micron in size, smaller than almost any sediment filter.

But ceramic filters aren’t good at removing chlorine, heavy metals, chemicals, or other dissolved contaminants. They are best when paired with a standard sediment filter, a carbon filter, or both. This allows for much better purification than ceramic alone.

Other Filter Types

There are a variety of other filter types you may wish to include in your system. You might add a UV filter to eliminate viruses and bacteria, or an ion-exchange resin stage to remove heavy metals. In many cases, you’ll still want to pair at least a sediment filter with these. 

Assembling the DIY Under-Sink Water Filter

Once you have your water test results and have decided what you want to remove and how many stages you’ll need and you’ve gathered the components, it’s time to assemble your new water filter and connect it to your cold water line. The main steps to this are:

  1. Place the filter cartridges into the sumps and attach the sumps to their caps.
  2. If you’ve decided on a multi stage design, connect ½” tubing between each sump, running from one output port to the next sump’s input port so that water passes through each stage. Make sure to align your under-sink water filters in the correct order.
  3. For ease of installation and to keep the sumps inline together, you may want to install the sumps on a mounting panel or bracket. 
  4. Screw your mounting panel or separate filter sumps of your under-sink water filtration system in place under your kitchen sink.
  5. You’ll need to connect your under-sink water filtration system to the existing water supply. If your new DIY filter will have its own dedicated faucet, you’ll probably need to use a t-adapter to connect to the cold water line supply valve. Connect the existing faucet to one output of the adapter and the water filter to the other side. You may also want to use a bypass valve to connect your new water filter.

Is It Worth the Effort to Build a DIY Under-Sink Water Filter?

If you’re contemplating building a DIY under-sink water filter, consider whether it is worth the effort. After all, you can run to the hardware store or go online to buy a proven, compact under-sink water filtration system for a reasonable price. 

Pre-made under-sink water filters from companies like Aquasana or Whirlpool require a lot less plumbing knowledge than the DIY route. They’ve spent years and a lot of money developing a system that is easy to install, removes most contaminants, and works in a reliable and safe manner. Will your DIY water filter be that reliable and do as well at filtering your water?

If you are inspired to work on a plumbing project and you want to save money, this could be a worthwhile project. While you won’t have the warranty you’ll get from a pre-built water filter and your filter won’t be proven and tested, you could end up with a great filter and it could be a very satisfying accomplishment.

In Conclusion

While building a DIY under-sink water filter can be a lot of work, it’s not too hard for someone handy with tools who has a little plumbing experience. You may save some money compared to buying a pre-built system. Your resulting filter may even outperform the available under-sink water filtrations systems and you can customize it to suit your needs. 

Whether the work involved is worth it to you is a question only you can answer. We’ve provided a step by step guide and given you some things to consider. Before making a final decision, you may want to check out some of the filters on our list of Best Under-Sink Water Filters

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Craig Smith
Craig got his start in water working in the swimming pool and spa industry. Water treatment would grow into his main career but he ended up working in the pool industry for over 26 years where much of his time was spent balancing the water in customer's swimming pools and installing water filtration equipment. Craig offers an abundance of water treatment knowledge after helping homeowners get pure water for 26 years.

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