Under Sink Water Filter Low Pressure & Slow Flow Rate Fixes

Is your under-sink water filter sending only a trickle of water out of your faucet? Is it suddenly taking twice as long to fill a glass? Sounds like you’re dealing with a water pressure issue.

There are a handful of reasons why your under-sink water filter might be causing pressure or flow rate issues. In this guide, we’ll look at the possible causes of low pressure, and how to resolve the issue and bring your water flow right back up again.

📰 7 Causes of Low Water Pressure From Under-Sink Water Filter

Let’s look at the causes of low water pressure in under-sink water filters, starting with the most common:

Clogged Water Filters

Clogged water filters are the most likely cause of slow water flow. You probably noticed that your water flow reduced gradually over time. This happens as your filters gradually become more and more clogged with contaminants.

Most under-sink water filter cartridges have a lifespan of 6-12 months. Clogged filters don’t only reduce water flow; they also harbor the risk of bacterial growth, so it’s important to buy replacement filters as advised by the manufacturer.

Dirty and clogged cartridges

High TDS

If your water has a high level of total dissolved solids (TDS), your under-sink water filters will need to work harder to remove these contaminants from your water supply. Sediment and hardness minerals are two of the most common causes of slow-flowing water during the filtration process.

Obstructed Water Line

The tubing connecting your filter system to your cold water line might have a kink or an obstruction that’s preventing a full flow of water from passing through. Check the tubing for issues and make sure there aren’t any sharp bends from the tubing to the faucet.

Poor Incoming Pressure

If your home’s own water pressure is low or sporadic, that might be why your drinking water supply has a slow flow. Check whether you’re also experiencing a pressure dip in your other sinks or showers.

Restricted Aerator

Your faucet aerator itself might be the cause of reduced pressure. When this aerator becomes clogged with debris, it reduces how much water can leave the faucet, giving a false impression that the water filter system is to blame.

Clogged faucet aerator

Faulty or Plugged Valves

There are multiple valves in any filtration system, including dual check valves, pressure limiting valves, and self-piercing saddle valves. If any of these valves become clogged or faulty, or are only partially pierced (applicable only to a self-piercing saddle valve), they may cause your tap water flow rate to drop.

Limited System Design

The design of the filtration system itself might be the cause of slow-flowing tap water. Some systems can’t operate at high pressure, so they have a pressure limiting valve to prevent damage from fast flow rates. These systems have slower flow rates than other filtration systems, and unfortunately, there’s not much you can do about it.

📥 6 Causes of Low Water Pressure From Under-Sink Reverse Osmosis System

There are a few reasons why a reverse osmosis system might reduce pressure and flow rate:

Faulty Or Old Water Tank

Reverse osmosis systems have a water storage tank that stores filtered water. This means that when you open the faucet, you get filtered water on-demand from a separate faucet, rather than having to wait for the water to pass through the water filtration system.

The water storage tank has a limited lifespan. The tank itself or its internal parts can erode and become faulty after so many years of use. This may affect the flow of water leaving the RO system.

Faulty and old ro water tank

Empty Storage Tank

You might notice a reduced flow of water due to a complete lack of water in the storage tank. To get water into the tank, check that all ball valves and inflow valves are open. Make sure the tank’s pressure is at 8 PSI to allow water to enter.

High or Low Tank Pressure

Storage tanks for RO systems need a pressure of around 8 PSI. If the pressure is too high, the amount of water flowing into the tank will be restricted. If the pressure is too low, the water won’t leave the system at a fast enough rate.

To resolve a tank pressure issue, empty and repressurize the tank to achieve 8 PSI.

Burst Air Bladder

A burst or ruptured air bladder in your RO system causes flow rate to slow to a trickle. The only way to resolve this is to replace the water storage tank in the reverse osmosis system. Hire a plumber or a water technician to assist with the process if needed.

Valves Switched Off

The restrictor valve and check valve in your reverse osmosis system should always be switched on. If any of these are turned off or clogged, your water flow will be lower than normal. Make sure these valves are switched on at all times to deliver an uninterrupted flow of water from the system.

Checking the flow restrictor

RO Filters Clogged

Finally, reduced pressure or water flow might be caused by a clogged activated carbon filter, sediment filter, or RO membrane. If you notice a decline in your water taste along with reduced flow, clogged filters are probably the cause.

⚙️ How to Resolve Poor Water Pressure Caused by Under-Sink Filtration System

Replace the Filters on Time

The best way to keep your pressure and flow rate at adequate levels is to replace the filters when they reach the end of their filter life.

Some under-sink filter systems have a light that lets you know when a filter replacement is needed. If your system doesn’t remind you, you’ll need to make a note in your calendar and replace the filters on or before the end of their lifespan.

Consider Installing Additional Water Treatment Systems

It might seem like installing yet another water treatment system will only slow down your flow rate even more, but this isn’t true. In some cases, installing an additional filter can actually improve your flow rate.

For instance, installing a dedicated sediment filter at your point of entry is a good idea if you have high-sediment well water. It’ll prevent a slowdown of water flow and protect your under-sink filters from damage.

Whole house sediment filter install

Additionally, a water softener can prevent limescale formation in your under-sink filter system, which also affects the speed of water flow.

Ensure your Incoming Pressure is Adequate

You need a water pressure of at least 60 PSI for your home’s appliances to be able to function properly. Check your pressure gauge and speak to your water supplier if you think there might be a problem caused by the water distribution pipes.

Consider hiring a plumber to install a booster pump if the problem is isolated to your home.

Clean Out your Faucet Aerator

In the case that poor flow is caused by a clogged aerator, take the faucet apart and remove any debris from the internal parts and aerator screen. Once you’ve cleaned the aerator, secure it tightly back in place to prevent leaking.

📑 Takeaway

Any kind of filtration system installed underneath your kitchen sink will reduce your flow somewhat. But if your water starts to leave your main faucet in a trickle, you’re probably dealing with one of the issues mentioned on this list.

If in doubt, contact the manufacturer of your system. They should be able to help you resolve your issues with water flow if you can’t diagnose the problem yourself.