How to clean a water tank safely

How often?

We found no national rule for homes in India. About every six months is a sensible habit, and it’s what a Jammu education department circular asks of school tanks. Clean sooner after a flood, after dirty water or if you see sludge. Tanks filled by tankers need extra care.

The steps

1. Save enough clean water for drinking and cooking, then shut the inlet.
2. Use up or drain the tank, and open the taps to clear the pipes.
3. Scrub the walls and floor, then remove the sludge and rinse.
4. Disinfect, then flush the pipes through each tap, and let the water stand before you use it.
5. Check that the lid fits tightly, and that overflow pipes and vents are covered with mesh.

Disinfecting

Tamil Nadu’s flood guidance tells workers to scrub tanks with bleaching powder, chlorinate them to 2 parts per million, and wait an hour before use. WHO emergency advice is to disinfect with the tank only a quarter full, because more water dilutes the chlorine.

Those are guides for emergencies, and bleaches vary in strength. Follow the product’s label, or use a professional service.

Stay safe

Going into a sump can kill. Air in closed tanks can be dangerous, and strong chlorine fumes make it worse. Never go in alone, keep the lid open for air, and keep someone outside who can get help. For an underground sump, it’s safest to hire trained cleaners. Never mix bleach with other cleaning products.