Your RO System Is Making Little or No Water: Causes and Fixes

Customer question

"My reverse osmosis system is making little or no water / my tank won't fill / output is a trickle."

Answer

In most cases this is not a dead membrane. The two most common causes are clogged pre-filters and low storage-tank air pressure, and both are inexpensive and easy to check yourself. Work through the causes below in order, from cheapest and easiest to more involved. Diagnose before you replace anything.

Start with the pre-filters and the tank, confirm the membrane with a meter before buying one, and leave the advanced internal parts for last.

Steps

Work top to bottom. Each step is ordered by how likely it is to be the cause, starting with the cheapest and easiest.

1. Clogged pre-filters (most common)

A membrane is only as good as what sits in front of it. Pre-filters protect the membrane, and when they clog, flow to the membrane drops and production falls off.

How to check: Look at how old the pre-filters are. If they are older than about 12 months, or you do not know when they were last changed, assume they are clogged.
How to fix: Shut off the feed-water valve and the tank valve. Open the RO faucet to release pressure. Swap the pre-filter cartridges, inspect the O-rings while the housings are open, then reassemble. Run the system to flush for about 10 minutes before using the water.

2. Low storage-tank air pressure

A tank that feels full but only delivers a trickle is the classic symptom of low tank air pressure. The tank uses a pressurized air bladder to push stored water out to your faucet.

How to check: Turn off the feed water. Drain the tank fully through the RO faucet. With the tank empty, read the air valve (usually on the bottom of the bladder tank) using a low-PSI gauge. As general guidance, an empty tank usually reads roughly 6 to 8 PSI.
How to fix: With the tank still drained, add air with a hand pump or bicycle pump to about 7 PSI. Do not overinflate. As general guidance, going above about 10 PSI can damage the bladder. If water sprays out of the air valve when you check it, the internal bladder has ruptured and the tank needs to be replaced.

3. Exhausted RO membrane

If the pre-filters are fresh and the tank pressure is correct but production is still low, the membrane itself may be worn out. This is more likely if the membrane is 2 or more years old.

How to check: Use a TDS meter. Compare the TDS of your feed water against the TDS of the filtered (permeate) water. If the difference between the two has dropped well below what the system used to deliver, rejection has fallen and the membrane is likely spent.
How to fix: Replace the membrane. Flush a new membrane for about 30 minutes before using the water. Match the membrane class to your feed-water TDS only if that is relevant to your setup. Do not over-spec it.

4. Low inlet (feed) pressure

RO production depends on incoming water pressure. As general guidance, an RO system wants roughly 40 to 80 PSI of inlet pressure. Below about 40 PSI, production drops sharply. This is common on well systems.

How to check: If your home or well runs at low pressure, or production is chronically slow with healthy filters and tank, suspect feed pressure.
How to fix: If low feed pressure is chronic, add a booster pump ahead of the RO system to raise the inlet pressure.

5. Clogged check valve or flow restrictor (advanced)

If you have ruled out causes 1 through 4, a clogged check valve or flow restrictor can stall production. This is the advanced step and is reached only by elimination.

How to check: The check valve is located near the membrane housing. The flow restrictor is on the drain line. A blockage in either can stop the system from making water.
How to fix: Clean or replace the affected part. If you are not familiar with these components, escalate to support rather than guessing.

Safety / before you start

Always depressurize the system before opening any housing. Shut off the feed-water and tank valves, then open the RO faucet to release pressure.
Do not overinflate the storage tank. Too much air pressure can damage the internal bladder.
This guide covers standard under-sink and point-of-use RO systems. Whole-house or commercial RO should be routed to Crystal Quest engineering rather than handled by DIY guesswork.

When to contact support

Reach out to Crystal Quest support if:

Water sprays out of the tank air valve, which means the bladder has ruptured and the tank needs replacement.
You have confirmed low rejection with a TDS meter and suspect the membrane.
You are not comfortable locating, cleaning, or replacing the check valve or flow restrictor.
You have a whole-house or commercial RO system. These should be reviewed by Crystal Quest engineering, not diagnosed by trial and error.