On a tank system, check tank pressure, automatic shutoff and check-valve function. On a tankless system, distinguish normal programmed flushing from truly continuous drain flow.
Automatic shutoff valve
Traditional RO systems use an automatic shutoff valve to stop feed water when tank pressure rises. A failed or incorrectly plumbed valve can allow continuous production and drain flow.
Tank or check valve problem
If the tank never reaches the pressure needed to trigger shutoff, the system can continue running. A failed check valve can also prevent proper pressure isolation.
Tankless flush cycles
Tankless systems often flush the membrane automatically. Short intermittent drain events can therefore be normal even when no water is being dispensed.
Why this matters for ownership cost
A malfunctioning RO system can waste far more water than its advertised production ratio suggests, making troubleshooting financially important.