What causes a high salinity alarm on your watermaker?

A high-salinity alarm means your watermaker's product water isn't clean enough to send to the tank. It's usually one of a small number of causes — and only one of them is a dead membrane.

1. Pressure-vessel O-ring leak

The end-cap O-rings on the pressure vessel let a tiny amount of feed water bypass the membrane and mix into the product stream. Very common, often overlooked, and cheap to fix.

2. Salinity probe drift

Probes fail slowly. A quick calibration check tells you whether the water is actually salty, or the probe just thinks it is.

3. Low operating pressure

Membranes reject salt more efficiently at correct pressure. If the regulator has drifted or the high-pressure pump is worn, salinity climbs.

4. Fouled or aged membrane

If the O-rings, probe, and pressure all check out, the membrane itself may be at the end of its life.