DIY Under Sink Water Filter – Step by Step Guide

Author: Jason Hollow - Published: 2021/09/22 - Updated: 2023/01/05

Disclaimer: This page may contain affiliate links. If you buy a product or service through an affiliate link, we may earn a commission but at no additional cost to you. You can view our full affiliate disclosure here.

To build your own under sink water filtration system, you need a proper game plan, plumbing knowledge and a lot of time on hand.

This brings us to the question: will a DIY under sink water filter be as neat, efficient and safe as one from a reputed brand? Well, there’s no subtle way to break the news – maybe yes, maybe not!

If you’re still up for it, we are here with a detailed guide that will help you pull it off. We walk you through all the supplies you need, various filter cartridges and how to put everything together.

So, here is our step-by-step guide on how to build a DIY under sink water filter!


  1. Check to see if you have all the necessary supplies and tools.
  2. Test your water for contaminants and minerals so you are guided accordingly as to what filter type(s) you need to use.
  3. Use a standard-sized filter housing and filter cartridge. You can also combine multiple filter stages. Pro tip: It is always better to choose NSF-certified components.
  4. Underneath the kitchen sink, properly mount the filter unit near or adjacent to the cold water line.
  5. Connect the DIY under sink water filter to the feed water.
  6. Attach the outgoing water supply from the system to the sink faucet.

Is DIYing Worth the Trouble?

Under sink water filters are state-of-the-art appliances that feature many aspects of modern technology. Not only do they purify your water, but most are also compact, sturdy and comply with food and safety health standards.

They may seem like an investment upfront, and it’s tempting to build one yourself to save money, but we suggest you rethink your decision. While you may find the process non-intimidating, unfortunately, there is no easy way to test if your homemade under sink filter is actually working.

Not to forget, accredited brands employ years and years of research and development to bring you a system with a user-friendly interface. Then, they undergo testing to certify that the products actually work.

In case of any malfunctioning, you won’t have the support of professional customer service representatives either.

On top of that, the process of building an under sink water filter from scratch involves the use of multiple power tools and supplies that may not be beginner-friendly. Thus, you may end up exceeding your budget anyway.

On the other hand, if you are familiar with plumbing supplies, have had poor experiences in the past with water filters or just fancy a DIY project, you definitely should give it a go!

How to: DIY Under Sink Water Filter

DIY Under Sink Water Filter Thumbnail

All arguments aside, let’s move on to DIY water treatment systems.

What’s in Your Water?

Testing the source water is the first step towards building an under sink water filter. In fact, it is the first and most crucial step even if you decide to purchase a system from reputed brands like Clearly Filtered or Aquasana.

Unless you know the level of contaminants in your water, you’ll end up with a purification system that doesn’t address your individual issues.

The easiest (sadly, not the most reliable) route to take is to check the Consumer Confidence Report issued by your municipal water supply board. You can find a free-of-cost copy online at

Another option is to send a water sample to a certified laboratory. A private laboratory will charge you anywhere between $50-$500. Remember, it’s impossible to check for all contaminants at the same time, so choose wisely.

If you want the results in a pinch, a home water testing kit is your best bet. You can buy it for as low as $20.

Tools and Supplies Needed for Making Your Own Under Sink Water Filter

Here is a list of all tools and supplies you will need to make your own under sink filter system.

  • Filter sump(s)
  • Filter cartridges(s)
  • Mounting panel
  • Tubing
  • Connectors
  • Bypass valve
  • Water filter wrench
  • PTFE tape
  • O-rings

Filter Sumps (Single or Multi-Stage)

It’s time to put your water test results to use. Identify the contaminants you want to remove and decide whether you need a single-stage or multi-stage filtration system.

Buy ten-inch-long filter sumps with a mounting panel and align them together.

Types of Filter Cartridges

Depending on the contaminants in your water, you can select from a wide range of under sink water filter cartridges.

Here, we shall discuss the most commonly used cartridges for residential water treatment systems. Remember to look for NSF-certified filters to ensure they work as advertised.

Sediment Filters

If you can see traces of suspended solids in your tap or well water, a sediment filter is the best choice for you.

Sediment filters act like a barrier to restrict dirt, rust, clay, silt or sand particles from entering your water glass.

Some very fine sediment filters can also remove bacteria and cysts such as cryptosporidium and giardia.

Sediment filters are rated in microns, which indicates the pore size of the filter screen. You can find various under sink sediment water filters ranging from 1 to 50 microns.

Granulated Activated Carbon (GAC) and Carbon Block Filters

Carbon filters are one of the most commonly used filtration media that target the common complaint with tap water; poor taste and weird smells.

They improve water aesthetics by removing chlorine and many chemicals and organics. They will give you water that is much clearer in color and without a hint of unpleasant odor.

Moreover, some carbon filters are designed to reduce heavy metals like lead too. We recommend a minimum of 1 carbon-based filter stage to ensure efficient removal of all chemicals like pesticides.

two water filter cartridges dropped in water

Iron Filters

Even though iron is not hazardous to health, it is recognized as a secondary contaminant. If you haven’t tested your water, you might still be aware of the nasty metal’s presence.

If your water supply is high in iron, you will notice a metallic taste in your glass of water, tea, coffee and juices, etc. In addition, food cooked in iron-rich water may become discolored or develop an odd flavor.

You may also notice ugly reddish-brown rust stains on sinks, fixtures and clothes. Thankfully, adding a special iron filter cartridge to your DIY under sink water system will take care of the problem.

KDF Filters

KDF filters are mainly used in conjunction with carbon filters to target a wide range of contaminants. Besides reducing lead, mercury and iron, the redox reaction in the KDF media inhibits the growth of bacteria, algae and fungi.

Just make sure the cartridge is NSF-61 certified to ensure it is safe for use and will not leach unwanted harmful contaminants into your water.[1]

Other Filters

There are many other water filter cartridges available to target specific contaminants. For example, a UV stage will help deactivate bacteria, viruses and cysts. On the other hand, ion exchange resin will tackle a high level of heavy metal contamination.

Putting Everything Together

Now, it’s time to put everything together. First, insert the filter cartridges inside the sumps and twist them to the cap.

Then, connect the ½-inch tubings to the “in” and “out” ports on either side of the under sink water filter module.

The inflow tubing must be connected to the cold water line, and the outflow tubing goes towards the faucet.

We highly recommend installing a bypass valve to make maintenance easy.


In conclusion, DIYing an under sink water filter system can be a great project if you’re up to the challenge.

You should start by finding out more about your water supply quality.

Then gather all the tools, supplies and equipment you need.

Standard-sized filter sumps and cartridges allow you to choose from a huge selection of products, from sediment to KDF filters.

Lastly, all you need to do is assemble everything and put it to work.

Further Reading


Meet Jason Hollow

Jason Hollow Jason is the founder of Water Masterz and head of content creation. After six years in the industry, he has tremendous knowledge and first-hand experience on all things related to water treatment.

His credo: Not a single American should have to drink unhealthy water at home.

Leave a Reply

Your email address will not be published. Required fields are marked *

4 − 2 =