I agree that having clean water would help to improve the economy. If you believe that the market already exists for sanitation, then that is great! From the sound of it with the reduced costs for water purification from your system, it may be competitive even if you gave free access to the facilities to water customers.
I agree that wastewater treatment is an important part of the solution in creating an environmentally sustainable solution. However I feel that in order for it to be successful, it is also important that the solution be economically sustainable. I don't know for sure, but I don't think that there are any laws in place in India regarding wastewater treatment. I think that it is important to make wastewater treatment important enough to the people there that they would pay to use it. Otherwise a stable business in treating wastewater would be impossible regardless of how cheap it might be. I think that a phased-in approach would be most effective. First, focusing on areas that would be more willing to use wastewater treatment facilities such as in urban areas, and then phasing it to more rural areas would be the most effective. Building awareness about its importance over time.