Reverse osmosis systems producing little or no water almost always trace back to one of four causes: a clogged pre-filter (the most common single cause), insufficient incoming water pressure, a fouled or scaled membrane, or a storage tank that has lost its internal air pre-charge. Checking them roughly in that order — cheapest and easiest first — narrows the cause down quickly.
Check the pre-filters first
A clogged pre-filter is the single most common cause of an RO system that runs but produces little or no water — sediment and carbon pre-filters protect the membrane and are designed to catch exactly the debris that would otherwise foul it, which means they clog first. Check your system’s recommended replacement schedule and inspect the pre-filters even if you are not certain they are due.
Check power and the indicator light
On systems with a booster pump or electronic monitoring, confirm the unit is receiving power and check the indicator light’s status. A light showing a specific fault code (often “water shortage” or similar, depending on the brand) points toward the inlet solenoid valve or a low-pressure switch rather than the filters themselves — check your system’s manual for what your specific indicator pattern means.
Check incoming water pressure
| Pressure reading | What it means |
|---|---|
| Below ~40 psi | Insufficient to drive the RO process efficiently — a booster pump may be needed |
| 40–80 psi | Normal operating range for most residential RO systems |
| Above ~80 psi | May need a pressure-reducing valve; can accelerate wear on some components |
Disconnect the feed line at the system’s inlet to confirm water is actually reaching it at reasonable pressure — if incoming pressure is fine but nothing improves downstream, the problem is inside the system rather than the household supply.
Check the storage tank pre-charge
- Locate the air valve on the storage tank
Usually a small valve stem similar to a bicycle tire valve, on the underside or top of the tank.
- Check the tank is empty first
Drain the tank fully by running the RO faucet before checking pressure, since a full tank will give a misleading reading.
- Check the air pre-charge with a tire pressure gauge
An empty RO tank should read roughly 5–7 psi of air pressure — if it reads at or near zero, the bladder has lost its pre-charge and the tank cannot push stored water out efficiently.
- Re-pressurise to the manufacturer’s spec if low
Using a standard bicycle pump; if the tank will not hold pressure at all, the bladder itself has likely failed and the tank needs replacing.
When the membrane itself is fouled
If pre-filters are fresh, incoming pressure is adequate, and the tank pre-charge is correct, but production is still poor, the membrane itself may be fouled or scaled — a gradual process that happens even with proper pre-filtration over the membrane’s working life (typically 2–3 years, sometimes longer with good water conditions). Membrane replacement is a routine maintenance item on these systems rather than a sign of a defective unit.
Inlet solenoid valve or low-pressure switch
If the indicator light specifically shows a water-shortage or similar fault even when the household supply is confirmed adequate, the inlet solenoid valve or the system’s low-pressure safety switch may have failed, cutting off flow into the system as a protective measure. This typically needs a replacement part rather than a filter or pressure adjustment.
