The Good News: It's Usually Not the Membrane


Slow RO flow is almost always fixable — and most often the cause is a clogged pre-filter or a low-pressure issue, not a failed membrane. Here's how to diagnose it systematically.


Step 1: Check Your Pre-Filters First


Sediment and carbon pre-filters are the most common culprit for slow flow. When they clog, they restrict water reaching the membrane, reducing output significantly.


Action: If your filters are more than 4–6 months old, replace them first and test again. This solves the problem in the majority of slow-flow cases.


Step 2: Check Water Pressure


RO membranes require adequate feed pressure (typically 40–80 PSI) to operate efficiently. If your home water pressure is low, the membrane produces water slowly.


Signs of low pressure:

  • All taps in your home also flow weakly
  • Slow flow is worse in mornings or peak usage times
  • RO was installed without a booster pump on low-pressure supply

Action: A booster pump (typically ₹800–₹2000) installed before the RO pre-filters solves low-pressure issues. Many newer RO systems include one built-in.


Step 3: Check the Storage Tank


The RO tank uses an internal air bladder. If the air pressure is too low, the tank won't deliver water at adequate pressure.


How to check:

  • Disconnect the tank from the system
  • Check the Schrader valve (like a bicycle tyre valve) at the bottom
  • Correct pressure is typically 6–8 PSI (empty tank)
  • Use a bicycle pump to recharge if low

Step 4: Check the Membrane


If pre-filters are fresh, pressure is adequate, and the tank is correctly charged — the membrane may be fouled.


Signs the membrane needs replacing:

  • Output TDS is rising (rejection dropping below 90%)
  • System has been in use 12+ months
  • Flow is slow even with everything else checked

Diagnostic Order (in priority)


  • Check 1: Replace pre-filters if overdue
  • Check 2: Test input water pressure
  • Check 3: Check tank air pressure
  • Check 4: Measure output TDS and rejection rate
  • Check 5: Replace membrane if rejection is below 90%

Most slow-flow problems are resolved at step 1 or 2. Don't replace the membrane until you've eliminated the simpler causes.