Watertechadvice.com is supported by readers. If you purchase through referral links on our site, we make a commission at no extra cost to you. Learn more.

Home » Water Filtration Systems » Under Sink Water Filter Low Pressure (How to Fix It)

Under Sink Water Filter Low Pressure (How to Fix It)

By: Craig Smith
Published on:
Under Sink Water Filter Low Pressure-What to Do?

Does your under-sink filter with slow flow and low pressure make it seem like you can feel yourself aging as you wait for a glass to fill with water? 

It can be incredibly frustrating!

But you don’t have to worry about dinner getting cold or being late for work because of your slow water, you can fix it yourself. 

In this post, we’ll explain how to diagnose the cause of the slow flow through your filtration system. 

We’ll offer tips on how to take care of each problem to get your water flowing better, and we’ll discuss problems specific to reverse osmosis systems.

Causes Of Low Pressure And Flow With An Under-Sink Water Filter

There are a few reasons for under-sink water filter low pressure problems, as well as reasons for a slow water flow. We’ll go through these, giving tips on how to diagnose that problem and how to correct the issue.

Clogged Filters

Most manufacturers recommend a service life for the cartridges in their under-sink water filters. The problem is that you can use twice as much water in that time than the manufacturer expected during the filter life. 

Some under-sink water filtration systems monitor water usage, and the water filter may have a warning light to let you know when to change the filter. If that lights up, this is an obvious indication that you have clogged filters.

If you don’t have a warning light, then you’ll need to do more work to diagnose the problem. Remove the filter cartridges and examine them. A dirty cartridge is a sign you need to switch out your water filters. When the cartridges look clean, it’s likely that replacement filters won’t fix your slow water flow or fix the problem with too low water pressure from your under-sink water filter system.

If the filters appear clogged or dirty, filter replacement may correct the issue. Swap in some new filter cartridges and you should return your water pressure and flow to their former glory.

Water Quality

Low water quality can also lead to low pressure and slow flow, and the under-sink water filter may not be responsible. It could simply be doing its job, filtering your water supply as fast as it can. High mineral or sediment content can cause your under-sink filtration system to work much slower. 

This one is hard to correct on your own. Contact your local water department and find out if this is just a temporary change in water quality. If it is, you may need to wait it out. 

If this looks like a long-term problem, you may need to try a different filter cartridge media. That could mean a media that isn’t quite as fine. This may leave more minerals and sediment in your filtered water, but it would increase your flow.

Another alternative is to switch out your entire filtration system for one with a faster flow rate. These typically are physically larger and may have more or larger filter cartridges to allow more water through.

Water Line Kink

To diagnose a kink in your water line, inspect all the lines to and from your water filter to see if any of them make sharp turns or bends. Especially check the cold water line running to your under-sink water filter. This could cause a slow water flow rate and lower the pressure.

To fix the issue, try to reroute your water line. If a line looks damaged, you may need to replace that line. That should restore your pressure and flow to their correct levels.

Low/Fluctuating Incoming Water Pressure

Incoming water pressure plays a large part in how quickly under-sink filter systems work. Some under-sink water filters have pressure limiting valves. If yours has a pressure limiting valve, it can only filter at a certain rate and reduces pressure to match that. That may result in low water pressure from the filter, and it may not have anything to do with your incoming pressure.

Determine if water pressure in the whole house is low or if it is just the pressure in the kitchen or for the under-sink filter system.

If pressure to the entire home is problematic, contact your local water department and ask them about it. They may need to measure the incoming water pressure and inspect the water lines. 

If you have low pressure or slow flow in only the kitchen, it’s a different problem. It could be the pipes in your home or just a water line under the kitchen sink. You can shut off the water and check the water supply lines under the sink. If you don’t find any issue there, you may need a plumber to inspect the pipes within your home.

If nothing else works, you can install a water pressure pump on the incoming water line. This requires a professional plumber, so it is definitely a last resort.

Closed Valve


If one or more valves are closed, it will alter your water flow. You may have multiple valves under your sink, and you need to check them all. There could be a check valve, dual check valves, or ball valves. In those cases, fully opening them should fix things.

Self-piercing saddle valves could have another problem you need to check. It’s possible the valve only partially pierced the water line. That restricts the flow. Correct this by firmly closing the saddle valve to complete the piercing process. When you open it up, it should flow properly.

Clogged Aerator


If there is dirt or mineral deposits clogging the faucet aerator, that could cause a slow water flow rate or low water pressure. The aerator is a small screen that screws onto the end of the faucet. Even a partially plugged faucet aerator can reduce your flow.

To correct this problem, first remove the faucet aerator. Turn it upside down to empty any loose debris. Remove stubborn debris with a brush. You may need to soak the aerator in vinegar to remove difficult mineral deposits.

Problems Specific To Under-Sink RO Systems

Under-sink reverse osmosis systems have some possible additional problems that are specific to them. These are some of the common issues:

Low Tank Pressure

If the storage tank in your reverse osmosis system has a pressure that is too low then the water flow will be reduced. RO filters typically need around 8 psi of pressure in their RO storage tank to function properly.

To correct this issue, use a bicycle pump to add air. Check the pressure with an air pressure gauge frequently as you pump. You don’t want to overpressure the tank and cause damage.

High Tank Pressure

High pressure in your reverse osmosis storage tank, like low pressure, can affect how your reverse osmosis system works. To correct this problem, bleed air from the air bladder to lower the pressure. Once the air pressure is below 8 psi, your RO system should be good to go.

Ruptured Air Bladder

You’ll know your under-sink system has a ruptured air bladder if the water flow suddenly drops to almost nothing. Since the air bladder is not replaceable, the only way to correct this problem is to replace the entire storage tank.

Empty Tank

If you have no water in your storage tank, water won’t flow correctly. 

This is often caused by a closed valve. Make sure all the incoming water valves are completely open. Also use an air pressure gauge to check the tank pressure, as RO tank pressures over 8 psi can stop water from entering the tank.

One or More Valves Not Turned On

A clogged valve can reduce or stop the flow of water to a faucet. Double-check the valves to make sure they are completely turned on. If that issue persists, turn them off and on a few times to see if you can dislodge any debris.

In Conclusion

While under-sink water filter low pressure and slow flow rate can be a headache, don’t let it overwhelm you. In most cases, you can correct the problem yourself. Simply follow our tips above and you can easily diagnose and fix the problem causing your reduced performance.

If you are sick of the hassle and just need to buy a new filter check out the best under sink water filters here.

Photo of author
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.

Learn More About The Water Tech Editorial Team