Your RO is sending too much water down the drain

Does this match your symptoms?

• Drain line runs constantly or for long periods
• Noticeably higher water bill or faster tank depletion since installation
• Two or three litres to drain for every litre purified

Work through the causes in this order

Ordered by how often each turns out to be the real cause — not by what it costs to fix. 1 of these costs nothing to resolve.

1. Most commonTechnician job₹1,200 – ₹2,500

   1. Low inlet pressure forcing poor recovery

   How to confirm it

   Time a one-litre fill from the inlet tap. Slow filling means low pressure, and low pressure means the membrane cannot achieve efficient recovery — so proportionally more water leaves as concentrate.

   The fix

   Fit a booster pump. Recovery improves, membrane life improves, and the pump usually pays for itself in water and membranes.

   Part: Booster pump

2. CommonTechnician job₹1,500 – ₹3,500

   2. Scaled or fouled membrane

   How to confirm it

   A scaling membrane needs more cross-flow to shift the same concentrate, so rejection rises as it ages. Suspect it when wastage has increased alongside falling product flow.

   The fix

   Replace the membrane and address the cause — hard water without pre-treatment scales membranes quickly.

   Part: RO membrane

3. CommonTechnician job₹150 – ₹500

   3. Flow restrictor wrong or missing

   How to confirm it

   The flow restrictor on the drain line sets the reject ratio. If it has been replaced with the wrong rating or omitted after a repair, the drain will run far harder than designed. A technician can read the rating off the part.

   The fix

   Fit the correct flow restrictor for your membrane. A small, cheap part with a large effect on your water bill.

   Part: Flow restrictor

4. OccasionalTechnician job₹350 – ₹900

   4. Machine never cutting off

   How to confirm it

   If the unit runs continuously, the auto-cut-off or float has failed and it is producing and rejecting water around the clock. Symptom: drain line flowing even when the tank is full.

   The fix

   Repair the auto-cut-off or float switch. This is urgent — it wastes water continuously and shortens membrane life.

   Part: Auto cut-off / float switch

5. OccasionalYou can fix thisFree to fix

   5. Old-generation design

   How to confirm it

   Units more than about eight years old were frequently designed around 1:3 or worse recovery, before water efficiency became a selling point. If everything is healthy and recovery is still poor, the design is the constraint.

   The fix

   There is no repair for a design limitation. Capture and reuse the reject water, and prioritise recovery when you replace the unit.

   Part: None

When to stop and call a technician

• The drain runs when the tank is full — the auto cut-off has failed and is wasting water continuously
• Wastage has risen alongside falling product flow, which points at the membrane
• You want a booster pump sized and fitted properly rather than guessed at

When replacement beats repair

Costs shown are indicative bands for India, published so you can sanity-check a quote — they are not quotations, and they vary by brand, city and whether the technician is brand-authorised. Last reviewed 2026-08-08.