After more than 7,000 houses, we can usually guess what a tank will look like before the lid comes off. The details change with the area and the age of the building, but the same six findings turn up in almost every tank that has gone a year or more without a proper cleaning.

This article sets out those water tank cleaning Karachi results: what we see, why it happens here, what it means for the water at your tap, and how to check for it yourself. These are field observations from our own work, not a scientific survey, and we have kept numbers out of it where we have not measured them.

The six findings at a glance

What we find	Where	What it means	The fix
Dark sludge on the floor	Almost every tank, deepest underground	A store of sediment and bacteria that is stirred up at every fill	Vacuum extraction, then a schedule
Slime and algae on walls	Rooftop tanks with poor lids; all tanks near the waterline	Biofilm that protects bacteria from chlorine	Jet washing; a lid that blocks light
Rust and corroded fittings	Old steel lids, pipe entries, float valves	Discoloured water, metallic taste, gaps for dirt	Replace fittings; seal entries
Insects, larvae and animals	Tanks with cracked or missing covers	Direct contamination and mosquito breeding	Sound lid, mesh on vents and overflow
Signs of an earlier bad cleaning	Tanks that were “cleaned” recently	Acid-etched concrete, sludge pushed into corners, no disinfection	A complete clean, done in the right order
Years of neglect	Homes that have never had a cleaning	All of the above at once	A first deep clean, then every four to six months

1. A dark sludge layer on the floor

This is the most consistent finding. Every fill brings fine silt, rust and organic matter with it, and in still water it sinks. Underground tanks collect the most, because they receive water straight from the line, including the dirty first flow after every outage and repair.

The sludge is not just unsightly. It shelters bacteria, uses up any chlorine left in the water, and is disturbed each time the tank refills or runs low. When the level drops close to the outlet, it is drawn into the house. Where it comes from is explained in our guide to KWSB water supply, and the effect of outages in load shedding and water contamination.

2. Slime and algae on the walls

Run a hand along the inside of a neglected tank and it feels slippery. That film is biofilm, a layer of bacteria in a protective coating. It forms on any wet surface and thickens fastest in warm water. Where light gets in, through a cracked lid or a thin translucent plastic wall, green or black algae grow on top of it.

Rooftop tanks show this most clearly, because of the heat, as we explain in heat and bacteria in water tanks. In underground tanks the film is there too, usually as a brown coating at and below the waterline.

3. Rust and corroded fittings

Steel lids, ladder rungs, old pipe stubs and float valve arms rust steadily in the damp air above the water. The flakes fall in. Near the coast, in Clifton, Gizri and Seaview, salt-laden air corrodes lids, hinges and inspection covers noticeably faster. Corroded pipe entries also leave gaps where surface water and insects get in. A tank can be clean on the day and contaminated again within a month if these are not fixed, which is why every report we write lists them.

4. Insects, larvae and the occasional animal

Mosquito larvae are common in tanks with loose or missing covers. So are cockroaches, ants and lizards, and now and then a bird or a rat that fell in and could not get out. Householders are usually shocked, but the cause is always the same: an opening that was not sealed.

Larvae matter beyond the tank. The WHO’s dengue guidance tells households to cover, empty and clean domestic water storage containers because that is where the mosquito breeds.

5. Signs of an earlier bad cleaning

Many customers tell us the tank was cleaned a few months ago. Inside, we often find the evidence of how: concrete roughened by acid, which makes it hold dirt and film more easily; a clean patch within arm’s reach of the hatch and untouched walls beyond it; sludge swept into the far corners; and no sign that disinfection was done at all.

A manual cleaning without a vacuum cannot remove sludge, only move it. We describe the difference in tank wallah versus professional cleaning.

6. Tanks that have never been cleaned

Some families have lived in a house for ten or fifteen years without anyone opening the underground tank. Nobody was careless. The tank is out of sight, the water looked clear, and no one told them it needed doing. These jobs take longest: the sludge is deep and compacted, the film is thick, and the lid has often rusted through.

If this describes your home, do not be embarrassed about it, and do not send a labourer down to have a look. Tanks that have been closed for years are the most dangerous to enter. In June 2025, five men died in an underground water tank in Ibrahim Hyderi after the first two were overcome by gas.

Does it differ by area?

The six findings appear everywhere. What changes is the emphasis.

• Apartment blocks in Gulshan-e-Iqbal and Gulistan-e-Jauhar: large shared tanks with heavy sludge and no clear record of cleaning. See water tank problems in Gulshan and Jauhar.
• Bungalows in DHA and Clifton: big underground cisterns, corroded lids near the sea, and mixed tanker and piped water. See water quality in DHA.
• Older houses across PECHS, Nazimabad and North Nazimabad: ageing RCC with cracks and rough surfaces.
• Homes on borehole water in any area: thick mineral scale on walls and fittings.
• Tanker-fed tanks anywhere: more sand, and more variation from one visit to the next.

Water tank cleaning Karachi results: why tanks end up this way

The city receives a little over half the water it needs, delivered for a few hours at a time. A World Bank document describes supply ranging from two hours every two days to four hours a day at very low pressure, through a network that loses more than half its water. Intermittent, low-pressure supply through leaking pipes means sediment in every fill; storage for days means time for it to settle and for bacteria to grow; heat speeds everything up.

Check your own tank in five minutes

1. Lift the rooftop lid and look at the wall just above the water. Is it green, brown or slimy?
2. Shine a torch at the floor. Can you see it clearly, or is there a dark layer?
3. Look at the lid, hinges and pipe entries for rust and gaps.
4. Check for larvae: small wriggling shapes near the surface.
5. Open the underground hatch, stand back, and look from above only. Do not climb in.

If you see any of the six findings, the tank is due. Other warning signs, including those that show up in the family’s health, are listed in ten signs your water may be making you sick.

What we do about each finding

Our eight-step procedure deals with them in order: jet washing at 3,000+ PSI for the film and algae, vacuum extraction for the sludge, disinfection and rinse for what remains, and a photographed inspection for the rust, cracks and lids. A walk-through of a visit is in what happens during a professional tank cleaning.

The report you receive includes photographs taken inside your tank before and after, so you can see your own results and not just take our word for it. To book, contact the Gulshan and Jauhar branch or the DHA and Clifton branch, or get a price online. The organisations we clean for, alongside households, are on our clients page.

What your after photographs should show

The photographs in the report are your evidence. Look at them properly before you file them away.

• The floor: bare and even in colour, with no dark patches, especially in the corners and around the outlet.
• The walls: the same colour from top to bottom. A tide mark at the old waterline means the film was not fully removed.
• The ceiling and the underside of the lid: often forgotten, and often where algae and rust sit.
• Pipe entries and the float valve: clean, with any gaps or corrosion pointed out.
• Cracks and exposed steel: photographed close up, so a mason can see what needs doing.

If a provider cannot show you the inside of your own tank before and after, you have no way to know which of the six findings is still there.

Frequently asked questions

How much sludge is normal?

Some silt is unavoidable in Karachi, and a thin, even dusting after a few months is nothing to worry about. A layer you can draw a finger through means the interval is too long or the incoming water is unusually dirty.

My water looks clear. Could the tank still be dirty?

Yes. Sludge sits on the floor and film on the walls while the water above stays clear. It only shows at the tap when the level runs low or the tank is disturbed.

Will I get photographs of my tank?

Yes. Every job ends with a dated report that includes photographs from inside the tank.

How often should I clean after the first deep clean?

Every four to six months for most houses, as set out in how often to clean a water tank in Karachi.

Do newer buildings have cleaner tanks?

Newer concrete and plumbing help, but the sludge comes from the supply, not the building. A five-year-old tank that has never been cleaned looks much like a twenty-year-old one inside.

Is an underground tank always dirtier than a rooftop one?

It usually holds more sludge, because it receives water first. Rooftop tanks tend to have more algae and film because of heat and light.

Sources

External references used in this article, checked in October 2026:

• WHO: Dengue fact sheet
• Dawn, 11 June 2025: Five dead after inhaling toxic gases in water tank in Karachi
• World Bank, 2019: Karachi Water and Sewerage Services Improvement Project, project information document

About Khan Tank Cleaning

This guide is published by Khan Tank Cleaning, a Karachi water tank cleaning company founded in 2005 by Mateen Khan. We work from two branches, DHA Phase 2 and Gulshan-e-Iqbal, and you can read more about the company or contact either branch at any hour. Call or WhatsApp 0333 0293174 (DHA) or 0340 2717530 (Gulshan).