I am working as a Software Engineer in Bangalore.
There is a product called LifeStraw. It is a straw which filters the water, and makes it safe for drinking, as you suck through it. It costs about 3$ and I think it has a lot of potential in a country like India. We have written about it here: http://www.arewemad.net . You can also find more info about it here: http://www.lifestraw.com
It is only available through institutionalized purchase. Do you know any organization which will be willing to distribute this amongst the poor?