I've been working in India for 3 years and really only had 1 bad case of stomach upset which I put down to brushing my teeth with Mumbai tap water. I thought that as I didn't swallow it, I would be ok - mistake!
I've had the runs occasionally and sometimes a dry f@rt seems like a luxury, but on the whole I've managed to keep out of trouble by using bottled water for drinking, cooking and brushing teeth, ensuring food is well cooked, avoiding too much chili and washing my hands regularly especially before meals. I stay clear of the drugs mentioned, except for a packet of anti-diarrhoea tablets which I keep with me in case I get caught short while travelling.
You will be most susceptible if you are visiting India as your digestive system will be dealing with unfamiliar foods and to be honest, the food in the hotels can be a cause of grief.
And as someone said above, if you can't drink the water, the whisky is quite palatable!