How Often Should You Clean Your Water Tank?

The baseline: every six months

For a typical home on municipal supply, with an opaque plastic rooftop tank and a sump that are both properly covered, cleaning every six months is a sensible routine. In Delhi NCR, the two most useful times are:

• March–April, before summer. Warm water loses residual chlorine faster and bacteria grow more quickly. Start the hot months with clean tanks.
• September–October, after the monsoon. Sumps may have taken in muddy water, rooftop tanks may have collected rain and dust, and humidity encourages growth on tank walls.

When to clean more often

Move to every three to four months if any of these apply:

How often to clean an overhead water tank vs an underground one

Overhead tanks are exposed to heat and light, so biofilm and algae are the main concern. Underground sumps receive water first, so they collect the heaviest sludge. Neither should be cleaned without the other: an overhead tank refilled from a dirty sump is dirty again quickly. Our advice is simple — clean both on the same day, at the same frequency.

Clean immediately if you notice…

Don't wait for the schedule if:

• The water smells — musty, earthy, like rotten eggs, or of sewage.
• You see colour, particles, green specks or a film on water in a white bucket.
• Your RO pre-filter, tap aerators or shower heads clog much faster than usual.
• Anyone in the household has repeated stomach upsets you can't explain.
• You find something in the tank — a dead bird or rodent, insects, debris.
• Drain or flood water may have entered the sump.
• You've moved into a new home or the property has been empty for weeks.

If you suspect contamination, switch off the motor so it isn't pumped to the rooftop tank, and stop using the water for drinking and cooking until the tank is cleaned.

A simple schedule you can follow

An annual maintenance contract is the easiest way to stick to a schedule without having to remember.

Between cleanings

• Keep lids and manhole covers closed and sealed.
• Fit mesh on overflow and vent pipes.
• Shade a translucent tank or replace it with an opaque one.
• After a doubtful tanker delivery, clean sooner rather than later.

How often to clean an overhead water tank

How often to clean an overhead water tank depends on exposure: rooftop tanks in direct sun need cleaning every 3–4 months, shaded or loft tanks every 6 months. Clean after the monsoon whatever the schedule, and straight away if the water smells or looks cloudy.