Yes, the RO membrane is likely not filtering. Either it's not installed, or water is bypassing it due to a connection error.
- Immediate check: Open the stage 4 membrane housing. The blue RO membrane must be inside. If the housing is empty, install it now.
- Verify all tubing connections. One wrong connection can send tap water straight to the faucet.
- Test the TDS. Your tap water TDS and RO water TDS should not be the same. The system should reject over 90% of TDS. If they're similar, the membrane isn't working.
IF THAT DIDN'T WORK: If you get some TDS reduction but not 90%, water might be bypassing the membrane due to a faulty Automatic Shut-Off Valve or a bad membrane itself. You'll need to contact iSpring support to pinpoint it.