The lid was still open at 5:30am and the courtyard smelled like a swimming pool that had gone wrong. The cleaning gang had left at dusk. I put the motor on out of habit, then stopped. The first mug from the kitchen tap carried chlorine and something sweet-rotten under it. In a Delhi-edge colony or a Jodhpur haveli plot, that smell is how a “fresh tank” poisons a week of tea if you hurry.
A cleaned tank should smell of wet cement or almost nothing after a proper rinse. A sharp bleach bite means leftover disinfectant. A sewer smell means a drain backflow or a cracked wall toward the nali. A dead-animal smell is exactly that: a lizard, a rat, or a bird that the gang missed in a corner. Do not drink through it. Do not cook dal with it. Flush, find the source, then decide.
Home checks before you fill the overhead again
Keep the motor off. You do not want that water in the overhead and the RO. Open the lid with a torch. Look at the corners, the inlet, the outlet strainer, and the overflow. A torch finds a body. Your nose finds a drain.
Ask what they used. Many gangs pour cheap bleaching powder and leave a white cake. That cake keeps off-gassing. The tank needs rinse water, not more powder. If they used acid “to shine,” you have another problem: the water can stay harsh, and the plaster can suffer. Acid is a bad household habit.
Check the lid seal. A tank that “smells after cleaning” often smelled before because the lid never sat. Mosquitoes, dust, and a cat all visit. A new clean with an old gap is a waste.
Check the overflow. If it dips into a drain without a proper air gap, the drain can push smell and worse back when the nali is full in monsoon. That is not a perfume issue. That is contamination.
Smell the municipal inlet separately from the tank water if you can catch a bucket from the line. If the line already smells, the cleaning is not the only story. If the line is fine and the tank stinks, the tank or the leftover chemical is the story.
Do not mix a drop of leftover bleach water into the drinking matka to “make it safe.” Dose is not a guess on the kitchen floor.
Photos to take for the gang and for yourself
Photograph the leftover white powder, the lid gap, the overflow into the drain, and any dead creature they missed. Photograph the written chit if they gave one: date, chemicals, and whether they claimed a double rinse. Photograph a glass of the water against a white tile for colour.
If you will call a second cleaner, the first photos stop them from blaming you for a lizard that was always there.
If a child or an elder already drank a glass and feels sick, that is a doctor, not a blog step. Keep the glass photo. It is not a diagnosis. It is a timeline.
Neighbour timing on shared tanks and shared cleaners
In a duplex or a small apartment, one underground tank feeds two kitchens. Warn the other house before anyone makes tea. Shared tanks need a shared “do not drink” note on the fridge.
If the same gang cleaned the neighbour yesterday and their water is fine, your rinse was skipped or your overflow is unique. If the whole lane smells after the municipal line ran, the source may be the line. Ask who else filled at 5:30am.
A neighbour who dumps mop water into a yard drain that sits against your tank wall can pass smell through a crack. That is a mason and a polite war, not more bleach.
Complaint and repair path
Call the cleaning gang back for a rinse and a dead-animal check if they just left. Refuse a second full chemical dose as the first answer. Rinse is the first answer. Pump the tank out to a safe drain, not onto the neighbour’s wall. Refill from a known line or a tanker you trust, then dump that fill too if the smell remains. Two flushes are common. Three if they went heavy on powder.
If the smell is sewer, stop using the tank and call a plumber to inspect the overflow and any crack. A connection between a drain and a drinking tank is an emergency in household terms. Repair may mean raising the overflow, adding a flap that actually works, and sealing the wall.
Water test: a local lab can do a basic load. In many North Indian towns a simple potability test is the calm next step after the smell drops. Smell gone but family uneasy is a good reason to test. Smell still there is a reason not to drink, test or not.
RO does not make a sewage-contaminated tank fine. RO also hates heavy chlorine leftover. Change the prefilter if you accidentally ran it. Do not “clear the smell” by running the RO for an hour into the sink and calling it done.
If the gang damaged the waterproofing, call a tank contractor, not a mop. Use a safe drum until the tank is a tank again. Complain to jal board or PHED only if the incoming line is the stink.
Approximate INR rates that vary by ward
A household underground clean in many wards is Rs 800 to Rs 3,500 depending on size, how many men, and whether they pump out. A return visit only to rinse should be less, often Rs 300 to Rs 1,200, and you are right to argue if they left powder cakes. A basic lab test may be Rs 400 to Rs 2,000. A plumber to redo an overflow with a proper air gap might charge Rs 500 to Rs 2,500 in parts and labour. Waterproofing a leaking underground tank is a bigger band, Rs 5,000 to Rs 25,000 and up with size and how much they must empty and dry. A new lid and a lockable frame can be Rs 800 to Rs 4,000. Gated societies on the edge of a city pay more per visit because of entry hassle. Old mohalla cleaners charge less and may skip rinse unless you stand there. Stand there. Ward variation is real. A receipt is useful if the smell becomes a doctor bill argument later.
A tanker to refill for flushing is extra. Count it as part of cleaning.
FAQ
How long should a bleach smell last after a proper clean?
A light smell can linger a day after a real rinse. A sharp smell on day three means leftover powder or no rinse. Do not drink through a sharp smell. Flush again.
Can I add more phenyl to hide the rotten smell?
No. Phenyl in a drinking tank is a new poison. Find the body or the drain. Covering a sewer smell with perfume is how families get sick.
Is the water safe when the smell goes?
Safer than when it stank, not automatically safe. If the issue was leftover bleach and two flushes, many houses return to cooking use after the odour drops. If the issue was a drain or a dead animal, test and keep using a known safe drum until you trust the tank.
Should I run the motor to push smelly water out of the pipes?
You can flush pipes to the drain after you are sure the tank itself is being dumped on purpose. Do not fill the overhead as a “flush.” You will only move the problem upstairs and into the RO.
Short note
Paani Atka is not a jal board and not a lab. We are not certifying your tank as potable. The official water office is final for complaints about the municipal line. The lab slip is final for a test you paid for. If someone says the smell means you must bore a new well, that work still needs a local permit. Cleaning a tank is not a licence to drill.