The operational costs per litre of desalinated potable water is about 19 paise (roughly 1/5 of a USD cent). India currently have 4 desalination plants generating 36.5 million cubic metres of water annually. While India need approax 1400 Billion cubic metres of water annually. 

Now, you can understand how many more plants do India need if only dependant on them. 

Coinsreporter

econ

Water shortage to affect India's sovereign credit strength: Moody's

I don't understand why countries are hesitant on turning desalination to 11/10

Maybe India I get it it's cost. But e.g. California? Just pump tons and tons of desalinated seawater dude