Greetings As  Ratilal and ...

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Greetings

As  Ratilal and Guy suggested rainwater harvesting is a great source of water. If collected and stored properly potable in the tank. There additional filtration can be added. 

Let me know where the site is located and I can give you an idea of the water capacity. There is also the option to build a decentralized system to compliment the centralized system. Here is the link to a plan I have to do this in the form of a rainwater utility. 

Let me know if I can help.

Steve