It's no secret that those of us living in developed countries are extremely lucky. This point certainly proves true when we look at drinking water. The water that we take for granted is very hard to come by in most countries. And India is no exception.
Drinking water in India simply isn't safe for consumption by foreigners used to clean water. The water purifying facilities that we are used to don't exist in India.
So how can you stay safe? There are many ways, actually.
If you are going to be in the wilderness, or somewhere where there will not be an abundance of stores, then I strongly suggest you to invest in water purifying tablets. You simply pop a tablet into your water, and it purifies it. It lives up to its name :)
The most common option is to simply buy bottled water. This is a very safe method, as long as the bottle you're purchasing has a seal on it. Otherwise, you have no way of knowing whether the shopkeeper simply found a used bottle on the street and filled it up with tap water. Ick. Well-known names include Bisleri, Kinsley, and Dasani.
However, if you're staying in a home, the best option is just to boil water. It kills virtually all germs in the water, and is free! A word of caution, however- those of you staying in the northern regions at high eleveations, remember that water boils at a lower temperature in higher elevations, so you might not kill all the germs by simply boiling and drinking. Keep the water boiling for at least 5 minutes.