You're right about the beer - Kingfisher Strong - but did you know that all bottled water in India comes the Delhi and Mumbai municipal supplies? If you're in Mumbai the water in your tap is the same as in your bottle.
On my first trip to India - 8-9 months in '94-5 - I got really bad shîts twice. Both times was when I came down from the clean air of the mountains to the heat and dirt of the plains. {Manali to Delhi, then Kathmandu to Benares/Varanasi.}