RO reject flow is expected while water is being produced, but persistent flow after an apparent refill deserves a model-specific check. Watts RO-PURE lists feed conditions, tubing restrictions and tank air-charge problems among its possibilities. Confirm whether water is actually being drawn elsewhere before treating continuous drainage as a failed shutoff.
Establish whether the tank is really finished filling
Use the Watts Premier RO-PURE or Pentek RO-3000/RO-3500 procedure only when that is your system. A different valve arrangement, pump or tank may require different checks.
A tankless unit requires its own operating check. The APEC ROTL-600/ROTL-600PH automatic-flush guide distinguishes those named models’ programmed events from a storage-tank shutoff fault and from separate protection indications.
Note when drinking water was last drawn, and whether a connected refrigerator or ice maker has been using it. Do not assume the tank is full merely because it feels heavy or the faucet pours strongly for a moment.
If the tank has not accumulated a useful supply, begin with RO tank-not-filling checks. Slow production can keep the system working toward refill. The RO-PURE troubleshooting table treats low feed pressure and crimped supply tubing as possible causes of continuous operation.
If water is stored but the faucet is weak, use the separate full-tank delivery guide. Storage pressure and delivery need to be evaluated separately from membrane output.
Do not guess at a shutoff-valve failure
For its specific unit, Watts also lists feed pressure outside its requirements and excessive or insufficient tank air charge. A faulty shutoff may be investigated during service, but continuous drain noise alone does not prove that part has failed.
Ask a technician to document actual incoming pressure, tubing condition, tank charge measured empty as instructed, and whether the system stops producing when it should. The Pentek manual separately describes a membrane-output and reject-flow check. Measuring the correct streams under the prescribed conditions is more useful than substituting a new valve because water can be heard.
Do not plug the reject tube, clamp it closed or remove the air-gap protection to stop the sound. That changes the system's designed flow and drainage arrangements instead of resolving the fault.
What you can record safely
Record the duration and pattern of the flow, recent cartridge or membrane changes, and water use by any connected appliance. Photograph the system label and exposed tubing without disconnecting anything. If this started at a filter change, use the post-filter-change checklist.
Where a leak or uncontrolled discharge is causing damage, close the accessible RO feed according to the maker's instructions if you can do so safely, and arrange service. A drain flow fault is different from an external leak; the existing RO leak page explains that distinction. Return to normal service only after the actual cause is corrected and the manufacturer's commissioning checks are complete.