How an RO system makes water
Reverse osmosis uses household water pressure to push water through a semi-permeable membrane. Treated water (permeate) goes to a storage tank or, on tankless units, straight to the faucet. Rejected water (concentrate) goes to the drain. The EPA's WaterSense program describes this process and notes that RO output depends on pressure moving water across the membrane.
That means anything that lowers pressure or blocks the path slows the faucet: a loaded cartridge, a tank that has lost its air charge, or simply weak pressure coming into the house.
The usual suspects, in order
| Cause | Typical clue | First step |
|---|---|---|
| Clogged pre-filter | Flow faded gradually over weeks | Check the install date; replace per the manual |
| Low tank air charge | Strong flow for a few seconds, then a trickle | Follow the manual's tank pressure check (tank drained first) |
| Low house pressure | Other faucets also feel weak | Check the home's pressure and any main shutoff valve |
| Fouled or scaled membrane | Slow tank refill plus rising TDS at the RO faucet | Compare TDS readings; membrane replacement per manual |
| Kinked line or valve partly closed | Sudden change after cabinet work | Trace the tubing; open the tank and feed valves fully |
Simple checks you can do
- Look at the dates. If the pre-filters are past the interval in the manual, that is the most likely fix. See how often to replace RO filters.
- Open the tank valve fully. Under-sink cleaning can bump it partway closed.
- Check the tubing. Stored items can pinch a line against the cabinet wall.
- Give it time after use. A tank system refills slowly by design; after a big draw, flow is weak until the tank recovers.
- Compare other faucets. If the whole house is weak, the RO system is not the root cause.
When it is the tank or the membrane
Storage tanks hold an air charge that pushes water out. If that charge drops, the faucet spurts and then trickles even when the tank is full. Manufacturers describe how and when to check it, usually with the tank emptied first. Do not guess at a pressure number; use the one in your manual.
Membranes slow down as they collect scale or fouling. Hard water and skipped pre-filter changes speed this up. A membrane problem often shows up as both slower production and a higher TDS reading at the RO faucet compared with readings when the system was new. Our guide on what a TDS meter can tell you explains how to track that.
Cold water and season matter too
RO production is affected by water temperature as well as pressure, and manufacturers rate output at specific test conditions. Small seasonal changes are normal. A sharp, sudden drop is not, and points back to the list above.
When to call for help
Call if the flow stays slow after new pre-filters, if you see leaks at the tank or drain line, or if you are not comfortable draining and checking a tank. Jorge can look at the system, test your water, and explain whether hardness or sediment is shortening cartridge life. If the system is due for parts, he gives you an itemized quote after the free test. For Living Water's own unit, see the alkaline RO system.
https://www.epa.gov/watersense/point-use-reverse-osmosis-systems
https://www.epa.gov/system/files/documents/2025-01/ws-products-home-water-treatment-guide_v2_508.pdf
https://www.cdc.gov/drinking-water/prevention/about-choosing-home-water-filters.html
Updated 2026-10-17 · Living Waters · Jorge Canela, Water Quality Specialist