The answer is desalination plants. Look at rich water-stressed countries in the Middle East and North Africa. All of them use extensive desalination plants. India has lots of very smart engineers. I am sure you can build them. Another thing: India needs to build the equivalent of the California State Water Project to move water from wet areas to dry areas. (China did the same.)

+1 for moving water from wet areas to dry areas. But desalination plants comes at a huge cost.