This probably goes without saying: refrain from drinking tap water! Take every precaution possible, otherwise you *will* end-up sitting on the toilet with "Dehli-Belly" (or in this case the "Pakistan-Poopies") for a few days.
Main indications that you're in trouble are diarrhoea, gastroenteritis, vomiting & fever.
Bacteria are the most common cause of water-related diarrhoea: bacteria are responsible for approximately 85% of all cases, parasites about 10% & viruses 5%.
> Cryptosporidiosis ("Crypto") is a diarrhoeal disease caused by microscopic parasites (Cryptosporidium). The parasite is protected by an outer shell enabling it to survive for a long time outside the body.
> E. Coli O157:H7 or Enteroaggregative E. Coli (EAEC) is one of hundreds of strains of the bacterium Escherichia coli. Most strains are harmless, but this strain produces a powerful toxin that can cause severe illness.
> Giardiasis is another common illness caused by a one-celled, microscopic parasite Giardia intestinalis. Giardia are found in drinking & recreational water worldwide, also in all developed coutries.
Some points to remember:
> Use disinfectant gel for your hands as well as disinfectant wipes .
> Brush teeth with bottled water & keep mouth closed when showering.
> Don't have ice cubes in your drinks.
> Keep your hands away from your face & mouth.
> If possible, buy water in plastic bottles (the glass ones are re-used) & check whether the cap seal is intact! The safest beverages are those that are carbonated (7 up, Coca Cola, etc.)
> Eat foods that are freshly cooked & piping hot.
> Avoid tea or coffee, especially those with milk.
> If you're a non-meat-eater like myself, your chances of falling ill are already lower.
It is true that water of Karachi is not clean. So foriegner's who are not used to tape water must use bottled water. Dont drink tape water on the way. I have observed that people sometimes get gestro.
But it is also true that most of the locals,including me, use tape water without boiling or filtering and get no harm. So it may be due to environment or habit.
I agree with the tip that's already been given..just stick to sealed bottled water when your out simple as...and boil it for drinking at home. Don't drink from glasses always ask for a straw, people do get ill just by drinking from a glass up there so be extra careful.
Don't eat anything from the kiosks on the streets. You should also only cook with and drink bottled water. Even while avoiding these things you will probably still feel sick. Everyone is really nice and will offer you food all the time, especially when you visit their homes. After a while I didn't feel like eating ANYTHING, but I would take a small amount and just nibble on it a bit so as not to be rude. Travellers should take Pepto Bismol with them, but detox teas like Ballerina Tea and mint teas make you feel sooooo much better.
I ate some kind of chickpea soup from Sunday Bazaar and I was STILL sick from it when I got back home over a week later.
It's one thing to be careful of drinking water that is not bottled, but also keep in mind that any local juices usually use tap water. I made the mistake to drink sugar cane juice from a local merchant, and I was sick for 2 days after that.