How to Install a Water Filter Under the Sink


Installing a water filter under your sink is a great way to improve the quality and taste of your drinking water. Water filters remove contaminants like lead, chlorine, and sediment that can negatively affect the smell, taste, and safety of your water. Installing a water filter under the sink is a relatively easy DIY project that can be completed in just a few hours.

In this comprehensive guide, we will walk through all the steps needed to install a water filter under your kitchen or bathroom sink. We will cover choosing the right water filter, gathering the necessary tools and materials, shutting off the water supply, connecting the filter system, and finally restoring water flow once the filter is installed. With a little time and effort, you can have filtered water flowing from your tap.

Choosing the Right Under Sink Water Filter

The first step is selecting the right type of water filter for your needs. Here are some of the most popular options:

Activated Carbon Filters

Activated carbon filters are one of the most common types used under sinks. They use a specially processed carbon medium that adsorbs contaminants through a chemical attraction process. Carbon filters are highly effective at removing chlorine, sediment, volatile organic compounds (VOCs), and other chemicals that affect taste and odor. They do not remove dissolved minerals or salts.

Carbon filter cartridges need to be replaced every 3-6 months depending on usage. This type of filter is inexpensive and easy to maintain.

Reverse Osmosis Systems

Reverse osmosis (RO) systems use a multi-stage filtration process to remove up to 99% of contaminants. RO filters force water through a semipermeable membrane that traps particles larger than water molecules. They effectively remove heavy metals, minerals, microorganisms, and other particles.

RO systems require more installation work and have a slower water flow rate. The systems also waste more water than carbon filters. However, RO provides the highest quality filtered water.

Water Softeners

Water softeners work by removing magnesium and calcium ions that cause hard water. Softened water prevents scale buildup and improves the efficiency of soaps and detergents. Water softeners use an ion exchange process that substitutes sodium ions for the hardness-causing minerals.

Water softeners do not actually filter out other contaminants. They are useful if you have issues with hard water but want to install a separate filter to handle other impurities.

Sediment Filters

Sediment filters use a physical barrier like a screen to trap suspended particles in water. They effectively remove rust, sand, dirt and other sediment. Sediment filters extend the life and improve the effectiveness of other filter types that would otherwise get clogged by particulate matter. They do not remove dissolved contaminants.

Sediment filters are often used as pre-filters for reverse osmosis systems. They also work well on their own if you only need to filter out sediment from your water.

Now that you understand the most common under sink filter options, you can select the right system type and capacity to meet your water quality needs. Products are available in a range of sizes and filter capacities for 1-5 stage filtration. Carefully read product descriptions to choose the ideal water filter model for your situation.

Gathering the Necessary Equipment

Installing an under sink water filter system requires gathering a few key materials and tools ahead of time. Having these items ready will make the installation process go faster and smoother:

Filter Housing System

This includes the filter housing container, filter cartridge, housing head, connecting tubes and hardware. The housing system you need depends on the specific filter type and model you selected. Make sure to purchase a system designed for under sink installation.

The housing capacity should match your filtered water needs. For example, a system filtering the main kitchen faucet needs higher flow rates than one just for a spare bathroom sink.

Shut-Off Valves

You will need shut-off valves to temporarily turn off the hot and cold water supply lines during installation. The valves allow you to work on connecting the filter system without water pressure flooding the cabinet. Make sure the valves match your plumbing line size (likely 1⁄2 inch or 3⁄4 inch).

Adjustable Wrench

An adjustable wrench gives you the flexibility to loosen and tighten different sized connections. A 12-inch wrench with a wide adjustable range should cover most filter installation needs.

Teflon Tape

Teflon tape helps create a watertight seal between the filter housing and connector threads. Wrap a few layers of tape around any threaded connections. The tape compresses when the parts are tightened.

Emery Cloth

Emery cloth provides an abrasive surface for sanding down metal burrs or rough edges on the ends of pipes and fittings. Smoothing the contact surfaces helps prevent leaks.


Have a bucket on hand to catch any water that drips out of the plumbing lines when disconnecting and attaching hoses and fittings. This minimizes water spillage when working under the sink.


A flashlight helps illuminate the darker space under the sink area during installation.

Safety Glasses

Safety glasses protect your eyes from debris while cutting tubing and working with fittings.

Shutting Off the Water Supply

Before disconnecting any plumbing or starting installation, you need to shut off the water supply using the angle stop shut-off valves under the sink. Shutting off the water ensures you can work safely without water spraying out of the lines.

Follow these steps:

  1. Locate the water supply valve: The shut-off valve is typically on the main water supply line that runs up to the faucet. There are separate valves for hot and cold water. They are normally under the sink towards the back.
  2. Turn the water supply off: Turn the shut-off valve clockwise until tight. This stops incoming water to the faucet. Turn off both hot and cold water lines.
  3. Relieve pressure: Turn on the faucet to release any built-up water pressure. Let the faucet run until the flow of water stops completely.
  4. Check for leaks: Examine the area under the sink to make sure no water is still dripping out of the supply lines or valves. Tighten connections if needed to stop minor leaks.

With the water shut off, you can now start the filter installation process without worrying about water drainage issues. Leave the faucet open while installing the filter housing system. This allows any remaining water to drain out of the lines.

Connecting the Filter System

Connecting the under sink filter system involves cutting into the existing water supply line, installing a Y-connector to divert water through the filter, attaching tubing between the filter housing and faucet, and securing all the components in place. Follow these key steps:

Cut into the Supply Line

  1. Locate the point along the cold water supply line where you want to install the filter system. This is normally right after the shut-off valve.
  2. Use a tubing cutter to cleanly cut all the way through the supply line at the desired point. Make sure the cut is straight and smooth.
  3. Use emery cloth to sand down the cut ends of the supply line to remove any rough edges or burrs. This prevents leaks.

Install the Y-Connector

  1. Wrap Teflon tape 2-3 times around the threads on all connectors to prevent leaking.
  2. Install a Y-connector using compression fittings to connect to the cut supply line. Position the connector so that:
  • The single branch points toward the faucet
  • One side branch points to the filter system
  • The other side connects to the cut supply line leading to the shut-off valve
  1. Tighten all the compression nuts securely using an adjustable wrench. Do not over tighten.

Attach Filter Housing

  1. Place the filter housing in the desired installation location under or near the sink. Make sure tubing will reach.
  2. Connect one end of the tubing to the housing outlet using a compression fitting.
  3. Run the tubing from the housing outlet to the Y-connector branch. Cut to the correct length using a tubing cutter.
  4. Attach the tubing to the Y-connector using another compression fitting.

Connect Faucet to Y-Connector

  1. Run a section of tubing from the Y-connector single branch to the faucet. Measure and cut to length.
  2. Attach compression fittings to securely connect the tubing to the faucet and Y-connector.

At this point, all the filter system components should be connected together with tubing routed between them as follows:

  • Shut-off valve > Y-connector > filter housing > Y-connector > faucet

Use plastic zip ties as needed to organize the tubing and keep it secure under the sink.

Restoring the Water Supply

After completing the filter system installation, the final step is to turn the water back on and check for leaks:

  1. Make sure the faucet is still open. This allows air to escape from the lines.
  2. Slowly turn on the cold water shut-off valve to restore flow to the system.
  3. Let water run for a few minutes to clear any air bubbles. Check for leaks and tighten any connections that drip.
  4. Close the faucet once water runs smoothly without sputters.
  5. Turn on the hot water shut-off valve. Check for leaks.
  6. Turn on the faucet again and verify proper flow and operation.
  7. Flush the filter by running a few gallons of water through it to clear out any assembly dust or particles.
  8. If leaks persist, turn the water supply off again and verify the source. Re-tape leaking fitting threads as needed to improve the seal.

Once any minor leaks are addressed, your under sink water filtration system should be fully operational! You now have filtered water flowing on demand right from your tap.

How to Install a Water Filter Under the Sink: FAQ

Installing a water filter under your sink is a big project with lots of steps. Here are answers to some frequently asked questions:

Where exactly under the sink do I install the filter housing?

The filter housing can mount to the inside of the vanity cabinet, on the wall behind the sink, or along the back. Pick a location with enough room for the housing and tubing connections that is also easily accessible for future filter changes.

What do I do if my water supply line is chrome-plated or some other material?

You can still install a filter following the same basic process. Use compression fittings made specifically for your supply line material rather than the plastic tubing types.

How difficult is it to replace the filter cartridge when needed?

Replacing the filter cartridge is very quick and easy. Just unscrew the filter housing, remove the old cartridge, drop in the new one, and reattach the housing. No tools or plumbing work needed.

Can I install a filter on both hot and cold water lines?

You can install separate filter housings on both hot and cold lines, but it is generally only necessary to filter the cold water. Water heaters remove most contaminants, and filtering both is redundant.

How can I improve water pressure if flow seems slow after installing the filter?

Make sure tubing inside the vanity cabinet has no kinks or bends that restrict flow. Consider a filter system with larger tubing, or add a booster pump if pressure loss is significant.

Is it possible to install a filter myself if I have no plumbing experience?

Yes! Installing an under sink filter system is definitely a DIY-friendly project. No soldering or complex work is required. Just take your time and follow all instructions closely.


Installing a water filtration system under your sink provides clean, contaminant-free water right from your tap. While it takes a bit of effort and planning, this is a straightforward project that most homeowners can tackle themselves. The benefits of filtered water throughout your home make it well worthwhile!

Hopefully this guide covered all the steps involved and answered common questions about installing water filters under sinks. Be sure to select the right filter type for your needs, turn off water supply lines, and take care to make leak-free connections. With some simple tools and materials, you will have improved water in no time.