If I were to return to India – I last visited 32 years ago – I would pay more attention to the quality of the water, and take measures to ensure my drinking water was safe. (But then, my perspective was formed by developing hepatitis and spending three weeks in a hospital, having several cases of giardia, and requiring two years to recover fully after returning home.)
I would bring an electric "wand" to place in a metal tin to boil water. Plug it in, boil the water for 10 minutes, allow it cool somewhat, and drink up!
When electricity is not available, I would consider using iodine tablets to kill off the nasties in the water.
Staying at a fancy hotel is no guarantee that the water is safe, as I learned one fateful day!
As for where to go on your trip, you might want to consider organizing your destinations according to a theme that interest you: musical performances, religious temples, Moghal Empire architecture, hill stations, prehistoric sites, places where Gandhi walked, areas where people speak Dravidian languages… You get the idea…