Short answer: clean your water tank every 6 months. That is the schedule we recommend for every house in Karachi, for the underground tank and the overhead tank together. Clean sooner if your water comes from tankers or boring, if the tank is shared by a whole building, or if the water has changed colour, smell or taste.
Karachi Tank Cleaning has been cleaning tanks in this city since 2007, and our crews open four to five household tanks every day. This guide explains where the 6-month figure comes from, which tanks cannot wait that long, and how to tell when yours is overdue.
Recommended Cleaning Frequency
Use this table as your starting point. Find the row that matches your tank and your main water source.
| Tank and water source | Clean every | Why |
|---|---|---|
| House on KWSC line water, both tanks covered | 6 months | Silt and rust arrive every time supply returns after a gap |
| House that mainly buys tanker water | 4 months | Tanker water quality varies from load to load, and each delivery stirs up the tank floor |
| House on boring water | 4 to 6 months | Hard, salty water leaves scale that holds dirt on the walls and floor |
| Apartment building with shared tanks | 6 months at minimum, 4 months if filled by tankers | Many families, heavy use, and usually nobody checking the tank |
| Restaurant, school, hospital, mosque, office | 3 to 6 months | High daily use and a duty to the public; often an audit requirement |
| Factory or industrial tank | As the plant’s SOP or audit standard sets | We follow the client’s schedule and issue a cleaning certificate |
| New tank, new house, or a house left empty for months | Before first use | Construction dust, cement residue or stagnant water |
Underground and overhead tanks get the same interval, and they should be cleaned in one visit. If only the overhead tank is cleaned, the pump refills it from a dirty underground tank the same evening. Doing both together also costs less than two separate jobs, as our water tank cleaning charges show.
Why Every 6 Months in Karachi?
We know of no regulation in Pakistan that fixes a cleaning interval for household tanks, and the World Health Organization does not set one either. Its technical note on cleaning and disinfecting water storage tanks explains how to do the job, not how often. The 6-month schedule comes from Karachi’s own conditions.
The water often arrives contaminated
In 2017 a Sindh High Court judicial commission asked the Pakistan Council of Research in Water Resources (PCRWR) to test Karachi’s water. Of 118 samples, 107 were unsafe to drink, and 88% carried coliform bacteria above WHO limits. A water board official told reporters at the time that residents also had to play their part by keeping their underground tanks clean (Dialogue Earth).
Supply comes in gaps
Karachi needs about 1,200 million gallons of water a day and receives about 650, according to a 2025 PCRWR report (Geo News). Most neighbourhoods therefore get line water for a few hours on set days. Each time the lines refill, the first water carries loosened rust and silt. While a pipe sits empty, any leak near a sewer line can also pull sewage in. All of it settles in your underground tank.
Stored water gets worse, not better
Sindh’s household survey (MICS 2017–18) tested water at the source and again inside homes. E. coli was found in 79.1% of Karachi’s source water and in 85.5% of water at household level, as reported by Geo News. The water picks up more contamination between the supply point and the glass, and the tank is where it spends most of that time.
Heat speeds everything up
For most of the year the water in a rooftop tank is warm. Chlorine from the supply fades quickly in warm stored water, and bacteria and algae multiply faster. After six months a Karachi tank usually has a layer of silt on the floor and a slippery film on the walls. That film, called biofilm, shelters bacteria from chlorine. It is the reason chlorine added to a dirty tank does not make the water safe. The tank has to be scrubbed first.
Factors Influencing Cleaning Frequency
Six months is the baseline. Four things move a tank above or below it.
Your water source
- KWSC line water brings fine silt and rust after every supply gap. In streets with old pipes it can also bring sewage. If your water turns grey or smells after supply resumes, do not wait for the 6-month date.
- Tanker water is filled at hydrants, and its quality depends on the hydrant and on the tanker itself. It often carries sand and mud, and the force of each delivery lifts whatever has settled on the tank floor back into the water.
- Boring water in Karachi is hard and often brackish. It leaves a crust of scale on walls, floats and fittings. Scale is rough, so dirt and bacteria cling to it. Our guides to Karachi’s hard water problem and removing hard water deposits from tank walls cover this in detail.
Tank type and material
- Underground concrete tanks have their cover at floor level. Rainwater and street water can run in around the manhole cover, and a crack in the wall can let in groundwater or sewage. Rough concrete also holds biofilm more firmly than smooth plastic. See the pros and cons of underground water tanks.
- Overhead plastic and fibre tanks stand in direct sun. Thin or light-coloured tanks let light through, which feeds algae. Lids crack, warp or blow off, and then birds get in. A tank with a missing lid needs cleaning now and a new lid the same day. Read more on bird contamination in rooftop tanks.
How fast the water turns over
A large tank serving two people holds the same water for days, and stagnant water spoils faster. So does water in a house that stays locked for months. An oversized tank is a common cause of bad-smelling water in small households. If you are installing a tank, choose the right size for the number of people who will use it.
Where the tank sits
Tanks in low-lying streets that flood during the monsoon, or next to an old or leaking sewer line, collect dirt much faster than the same tank on higher ground. If floodwater has reached your underground tank’s cover even once, treat the tank as contaminated.
Signs Your Tank Needs Cleaning Now
Do not wait for the calendar if you notice any of these:
- Water that looks yellow, brown, grey or cloudy
- A sewage, rotten-egg or musty smell from the taps
- Sand, black specks or silt at the bottom of a bucket
- Worms, larvae or insects in the water
- Green or black growth on the tank walls
- Tap filters and shower heads that clog within days
- Repeated stomach illness, diarrhoea or skin rashes in the household
Clean the tank after any of these events as well, whatever the date:
- Sewage mixed into the line supply in your street
- Rainwater or floodwater entered the underground tank
- A dead bird, lizard or rat was found in the tank
- Construction, plastering or plumbing work near the tank
- You moved into a house and do not know when the tank was last cleaned
For a closer look at the warning signs, read signs your family may be drinking contaminated water.
What Happens When a Tank Is Left Too Long
Sludge on the floor and biofilm on the walls turn the tank into a place where bacteria grow rather than a place where water waits. The household then meets the same germs every day through drinking, cooking, brushing teeth and bathing. Typhoid, hepatitis A and E, and diarrhoea are the usual results, and children are affected first. We cover these in waterborne diseases common in Karachi and how dirty tanks affect children’s health.
One risk is specific to this city. Naegleria fowleri, the “brain-eating” amoeba, kills people in Karachi almost every summer. It infects through the nose during bathing or ablution, not through drinking. Health officials say that lack of filtration and chlorination of potable water is a major source of the infection, and that the germ cannot survive in clean, chlorinated water (Dawn, June 2025). After the city’s third death of 2026, health experts again advised residents to chlorinate both underground and overhead tanks (ARY News, July 2026). Chlorine only does that job in a tank that has been cleaned.
Neglect also damages the system itself. Sludge wears out pump seals, scale jams float valves, and blocked outlets lower pressure. The full list is in the dangers of neglecting water tank cleaning, and the less common bacterial risks are covered in our guide to Legionella in Karachi’s water tanks. The health case as a whole is set out in the importance of water tank cleaning for health and hygiene, and the gains in the benefits of regular cleaning.
The Best Months to Clean
Two cleanings a year work best when they are tied to Karachi’s seasons:
- March or April, before the heat. Bacteria, algae and Naegleria are most active from May onwards. Start the summer with a clean, disinfected tank.
- September or October, after the monsoon. Rain pushes silt and sewage into supply lines and underground tanks. Clean once the rains are over.
If you clean three times a year, add a winter visit in December or January. More detail is in the best time to clean your water tank in Karachi.
DIY Water Tank Cleaning
A small overhead plastic tank can be cleaned by a careful adult. Drain it, scrub the walls and floor with a stiff brush, remove all the dirty water, disinfect, and rinse. For disinfection, the WHO method is 80 grams of high-strength calcium hypochlorite granules for every 1,000 litres of tank capacity. Fill the tank, leave it for 24 hours, drain it, then fill once more with clean water, wait 30 minutes and drain again before use. Our step-by-step guide to disinfecting a water tank after cleaning goes through each stage.
Two warnings matter more than the method:
- Do not climb into an underground tank on your own. It is a confined space. Air at the bottom can be low in oxygen, and chlorine fumes collect there. The WHO note calls work inside tanks “difficult and dangerous” and says someone must stay outside while a person is inside. Our safety page explains how our crews handle tank entry.
- Never mix chlorine with acid, toilet cleaner or any other chemical. The mix releases toxic gas.
Professional Water Tank Cleaning Services
A professional job follows six steps: drain the tank, remove the sludge, pressure-wash the walls and floor, vacuum out the waste water, disinfect, and rinse. A standard house takes 2 to 4 hours. Each stage is described in our service procedure, and the disinfectants are listed on the cleaning chemicals page.
For most houses the charge is between Rs 2,500 and Rs 10,500, depending on plot size or tank capacity and on whether you have one tank or two. You can get your exact rate from the calculator on our water tank cleaning services page. You look inside the tank before you pay, and if something is not right we redo it under our service guarantee.
If you are deciding between doing it yourself and booking a team, see why to hire a professional tank cleaning company.
Keeping the Tank Clean Between Visits
- Keep both lids closed and sealed. Replace a cracked lid straight away.
- Fit mesh over the overflow and vent pipes so insects and lizards cannot enter.
- Once a month, look inside with a torch. Check the colour of the water and the tank floor.
- Check the float valve. A tank that overflows or runs dry stirs up sediment.
- Write the cleaning date on the tank or save it in your phone, and book the next visit when it falls due.
The full routine is in how to maintain your water tank after cleaning.
Frequently Asked Questions
Is cleaning a water tank once a year enough in Karachi?
For most homes, no. A year of interrupted supply, tanker deliveries and summer heat leaves too much silt and biofilm. Once a year is the bare minimum for a covered tank on reliable line water. We recommend every 6 months.
Do overhead and underground tanks need the same schedule?
Yes. Water passes through both, so a dirty tank at either end spoils the whole system. Clean both in the same visit.
Can I add chlorine tablets instead of cleaning the tank?
No. Chlorine is used up by the sludge and biofilm before it reaches the bacteria inside them. Chlorine works after cleaning, not in place of it.
I have a filter or RO plant. Can I clean the tank less often?
No. A filter treats only the water you drink. You still bathe, wash dishes and brush your teeth with tank water. A dirty tank also clogs filter cartridges and RO membranes faster. See filtration and cleaning in Karachi homes.
Why did dirty water come back a few days after cleaning?
A cleaned tank stays only as clean as the water that goes into it. Line water after a supply gap, tanker water and boring water can all bring fresh silt into a tank within days. That comes from the incoming water, not from the cleaning.
How often should an apartment building’s tanks be cleaned?
Every 6 months at minimum, and every 4 months if the building depends on tankers. Who arranges and pays for it is a separate question, answered in who is responsible for tank cleaning in Karachi apartment buildings.
How long will we be without water during cleaning?
A standard house job takes 2 to 4 hours. Book it shortly before your line supply day or tanker delivery, when the tank is nearly empty. Less water is wasted and the tank refills soon after the team leaves.
Book Your Tank Cleaning
If your tank has gone more than 6 months, or you do not know when it was last cleaned, it is due. Call 0313-2796778 at any hour, or send your details through the contact page. We clean tanks in every area of Karachi, from North Nazimabad and Keamari to Baldia Town.
About the author: Ahmar Shoaib is the founder of Karachi Tank Cleaning. He holds a BS in Chemical Engineering from Karachi University and has run the company’s cleaning and disinfection work since 2007. This article follows our editorial policy.
Sources: WHO Technical Note No. 3, Cleaning and disinfecting water storage tanks and tankers (WHO/WEDC, 2013); PCRWR water quality testing for the Sindh High Court judicial commission (2017), reported by Dialogue Earth; PCRWR report and Sindh MICS 2017–18 figures, reported by Geo News (May 2025); health officials’ statements on Naegleria fowleri, reported by Dawn (June 2025) and ARY News (July 2026).
