The clearest signs that a Karachi household is drinking contaminated water are stomach illness that keeps coming back, water that smells musty or of sewage, any yellow, brown or green colour, sediment in the bucket, and a tank that has not been cleaned for more than six months. The difficulty is that contaminated water often shows no sign at all. It can look, smell and taste normal and still carry the bacteria that cause typhoid and hepatitis.
This guide lists ten warning signs, explains honestly what each one does and does not tell you, and sets out what to do. It is general information, not medical advice.
The Karachi Water Reality: Why Your Tank Carries More Risk Than You Think
Karachi’s main supply comes from the Indus through Keenjhar Lake and from the Hub Dam. What happens between there and your glass is the problem.
- Not all of it is filtered. In 2018, filtration plant officials told a Supreme Court-appointed commission that not even half of the water supplied to the city was filtered (ProPakistani).
- Pipes leak beside sewers. When the Pakistan Council of Research in Water Resources tested 118 Karachi samples in 2017, 107 were unsafe and a third contained E. coli, which the lead researcher said indicated mixing of sewerage and drinking water (Dialogue Earth).
- Supply is intermittent. The city gets about 650 million gallons a day against a need of 1,200 million (Geo News). Pipes that stand empty draw contamination in, and the first flow after a gap is the dirtiest.
- Tankers fill the gap, from official hydrants, illegal hydrants and private bores, with no certificate of quality.
- Then it sits in your tank, for days, in the heat.
Storage is where a household’s own water gets worse. Sindh’s household survey found E. coli in 79.1% of Karachi’s water at source and 85.5% at household level, as reported by Geo News. That gap is the tank, the pipes inside the house and the way water is handled.
10 Warning Signs Your Karachi Water Tank May Be Contaminated
Some of these point strongly to contamination. Others have innocent explanations as well. Each entry says which.
1. Recurring Gastrointestinal Illness in the Household
This is the most reliable sign. If family members repeatedly get loose stools, stomach cramps, nausea or vomiting without an obvious cause, suspect the water.
The pattern to look for is that it affects several people, it keeps returning, it improves when you stay somewhere else for a few days, and it comes back when you return home. Shared food usually causes one episode. Shared water causes a series.
Children under five show it first and suffer most. See how dirty water tanks affect children’s health and waterborne diseases common in Karachi.
2. Water That Smells of Chlorine, But Not Consistently
A faint chlorine smell in line water is a good sign. It means some disinfectant has survived the journey. Pakistan’s standard is 0.2 to 0.5 mg/L at the consumer end (S.R.O. 1063(I)/2010).
The warning is when water smells of chlorine as it arrives and has none by the time it reaches your taps, or when the smell comes and goes. Chlorine that vanishes quickly in storage is being used up by something: sludge, biofilm or algae in the tank. Chlorine test strips will confirm it.
3. A Musty, Earthy, or Sulphurous Smell
- Musty or earthy: algae, or bacteria living in biofilm and sediment. Common in rooftop tanks that let in light. See preventing algae growth.
- Rotten eggs: hydrogen sulphide gas from bacteria in rotting sludge at the bottom of the tank. It means the sludge has been there a long time.
- Sewage: sewage has entered the supply line or the underground tank. Stop drinking the water immediately.
Any persistent smell means the tank needs cleaning. A sewage smell means today.
4. Discoloured Water (Yellow, Brown, Grey, or Greenish Tinge)
- Yellow or brown: silt stirred up from the tank floor, rust from iron pipes or a steel tank, or iron in boring water.
- Grey or cloudy: fine suspended dirt, often after supply resumes. If it clears from the bottom of the glass upward within a minute, it is only air bubbles.
- Green: algae in the tank.
- Black specks: rotting organic matter, perished rubber washers, or manganese from groundwater.
Fill a clear glass from the incoming line and another from a tap. If only the tap water is coloured, the tank is the source. If both are, the supply is, and your tank is now storing it. See common water tank problems.
5. White or Grey Scale Deposits on Taps, Kettles, and Shower Heads
This is hard water, which is very common with boring water in Karachi. Scale is not a sign of germs and is not harmful to drink. It matters for a different reason: the same crust is forming inside your tank, and its rough surface gives bacteria a protected place to grow and makes the tank harder to disinfect. If the water also tastes salty, it may exceed the national limit of 1,000 mg/L for dissolved solids. See Karachi’s hard water problem and dealing with hard water stains and deposits.
6. An Oily or Chemical Film on Boiled Water
A thin, dull film or white flecks on boiled water or tea is usually minerals from hard water. It is harmless.
A rainbow-coloured, oily sheen, or a smell of petrol, solvent or chemicals, is different. It can mean fuel or industrial contamination, most likely in bore or tanker water. Boiling does not remove chemicals. Stop drinking that water and have it tested by a laboratory. See the impact of industrialization on water quality.
7. Unexplained Skin or Eye Irritation After Bathing
Rashes, itching or sore eyes after a bath can come from bacteria and algae in dirty tank water. They can also come from hard water, soap, heat and many skin conditions, so this sign counts only alongside others. If several people in the house are affected and the water smells or looks off, the tank is a likely cause.
8. Dry, Brittle Hair and Dry Skin
Hard, salty water leaves mineral and soap residue on hair and skin, which makes hair rough and skin dry. It is a comfort problem caused by the water’s mineral content, not evidence of infection, and there is no good evidence that it causes permanent hair loss. Treat it as a pointer to hard water, and see sign 5.
9. Visible Sediment, Particles, or Floating Matter in Water
Sand, rust flakes, green strands, slime, insect larvae or anything else you can see means the tank needs cleaning.
- Sand and silt: tanker or line sediment that has built up on the floor.
- Slimy strands or flakes: biofilm or algae breaking off the walls.
- Larvae, worms or insects: the tank is open somewhere. Check the lid, vent and overflow.
- Feathers or droppings: birds have access. See bird contamination in rooftop tanks.
10. Your Tank Has Never Been Professionally Cleaned
If you cannot remember the last cleaning, or the answer is never, assume the tank is contaminated. Every tank collects sediment and grows biofilm. The only open question is how much. A tank left for years will have a deep layer of sludge and a thick film that no amount of chlorine or boiling downstream can make up for. See the dangers of neglecting tank cleaning.
The Hidden Pathogens: What’s Actually Growing in an Unclean Tank
| Organism | Illness | Note |
|---|---|---|
| Salmonella Typhi | Typhoid | A drug-resistant strain has spread in Sindh since 2016, with 69% of early cases in Karachi (WHO) |
| Hepatitis A and E viruses | Jaundice, liver infection | Hepatitis E can be fatal in late pregnancy (WHO) |
| Vibrio cholerae | Cholera | Outbreaks follow floods and sewage mixing |
| E. coli, Shigella, rotavirus | Diarrhoea and dysentery | The most frequent cause of illness |
| Giardia, Cryptosporidium | Prolonged diarrhoea | Cysts resist chlorine. Boil or filter. |
| Naegleria fowleri | Fatal brain infection | Enters through the nose, not by drinking (CDC) |
| Legionella, Pseudomonas | Pneumonia, skin and ear infections | Live in biofilm in warm tanks. See the Legionella threat. |
How these organisms survive inside a tank is explained in bacteria in Karachi’s water tanks.
Why Boiling Water Is Not Enough
Boiling drinking water is the right thing to do. It kills bacteria, viruses and parasites. It has four limits.
- It does not remove chemicals, metals or salt.
- It does not remove sediment.
- It does not treat the water you do not boil: the water for bathing, brushing teeth, washing dishes and vegetables, and ablution.
- It does not clean the tank. The source of the contamination is still there, re-seeding every fresh fill.
The same is true of a kitchen filter. It protects one tap. See filtration and cleaning in Karachi homes.
How Often Should Karachi Homeowners Clean Their Tanks?
| Your situation | Clean every |
|---|---|
| Line water, sealed tanks in good condition | 6 months |
| Mainly tanker water | 4 months |
| Boring water | 4 to 6 months |
| Shared building tanks | 6 months at minimum, 4 months if tanker-fed |
| Any of the ten signs above, floodwater or sewage in the tank | Now |
The reasoning is in how often you should clean your water tank in Karachi.
What Does a Professional Tank Cleaning Actually Fix?
- Sludge. Pumped and vacuumed out completely.
- Biofilm and algae. Stripped from walls, floor and corners with a pressure washer.
- Remaining germs. Killed with a chlorine-based disinfectant on the cleaned surfaces, then rinsed.
- Unknown damage. An empty, washed tank shows cracks, failed fittings and gaps around lids, which our crew points out so you can have them repaired.
It does not change the quality of the water that arrives afterwards. For that you need a clean tank and treated drinking water together. The steps are on our service procedure page and the disinfectants under cleaning chemicals.
What You Can Do Right Now: A Quick Home Assessment
- When were the tanks last cleaned? More than six months ago, or unknown, means they are due.
- Is the rooftop lid intact and tight? Go and look today.
- Are the vent and overflow covered with mesh?
- Is the underground cover sealed and above floor level?
- Can you see daylight through the tank wall? If so, algae will grow.
- Fill a clear glass from the kitchen tap. Hold it to the light, then smell it.
- Run a clean finger along the inside wall of the overhead tank. Slippery means biofilm.
- Has anyone in the house had repeated stomach illness?
If you want certainty, a laboratory test for total coliforms and E. coli is the proper check. The national standard is none detectable in 100 ml. For the routine that keeps a cleaned tank clean, see how to maintain your water tank after cleaning.
If you suspect the water is contaminated today
- Boil all drinking water for at least one minute, or switch to a trusted bottled supply.
- Use boiled water for brushing teeth and washing fruit and salad.
- See a doctor about anyone with fever, blood in the stool, jaundice or signs of dehydration.
- Have both tanks cleaned and disinfected.
- Find and fix how the contamination got in.
Frequently Asked Questions
How can I tell if my tank water is contaminated?
Look for repeated stomach illness, smell, colour, sediment and slime. For proof, have a laboratory test a sample for coliforms and E. coli.
Can contaminated water look clean?
Yes. Bacteria and viruses are invisible, and water is usually badly contaminated before it changes colour or smell.
Is a film on my tea a sign of dirty water?
Usually not. A dull film or white flecks are minerals from hard water. An oily, rainbow sheen or chemical smell needs testing.
Does hard water mean my water is contaminated?
No. Hardness is minerals, not germs. Scale does make a tank harder to keep clean.
Should I get my water tested?
Test if someone has been ill repeatedly, after flooding, when you move in, or if you use bore water for drinking.
Your Family Deserves Safe Water
If any of these signs match your home, start with the tank. Call or WhatsApp 0313-2796778 at any hour. We clean and disinfect tanks across Karachi, including North Karachi, Garden and Gulberg. Rates are on our charges page, and under our service guarantee you look inside the tank before you pay.
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: Judicial Commission on Water and Sanitation proceedings, reported by ProPakistani (January 2018); PCRWR testing (2017), reported by Dialogue Earth; PCRWR and Sindh MICS figures reported by Geo News (May 2025); National Standards for Drinking Water Quality, S.R.O. 1063(I)/2010; WHO Disease Outbreak News, Typhoid fever in Pakistan (December 2018); WHO fact sheet on hepatitis E; CDC, About Naegleria fowleri infection.
