The requirement here is something related with harvested rain water which is stored in one tank and fresh water stored at a higher level.

The building in consideration would have 2 levels and upper level has a small utility area for washing / terrace gardening etc. Roof of upper level catches the rain water and its first flush water is collected in a small tank installed in upper level. Excess rain water flows to a ground water recharge system.

This water so collected has to be flown to a pipe line connecting to outdoor hose / toilet flush which is primarily connected to fresh water tank, ensuring that a non returning valve safeguards the fresh water source from being mixed with first flush of rain water.

Now there are a few questions:

  1. As the intention is to consume the rain water first, would this setup work if same thickness pipes are used or would it require bigger pipe for rain water tank as the pressures would differ due to tanks being in different levels, of different sizes (RW tank is smaller) and quantity of water varies(RW level reduces with consumption and not refilled unless there is a rain).
  2. Considering RW tank is covered from direct sunlight(might still receive heat), would it develop germs / water creatures with time?
  3. Is there a possibility that germs so developed in RW can flow back to fresh water tank through a non-returning value or a manual closing valve is really needed?
  • Rather than 2 tanks, maybe you could use one tank which has a fresh water feed controlled by a float valve. As long as the RW is above the float, fresh water never would be used. If RW were below that, you'd only use as much fresh water as actually consumed. – StayOnTarget May 12 '18 at 17:08
  • Hello, and welcome to Stack Exchange. Where in the world are you? Beyond practicalities, I suspect that local codes will have something to say about this. – Daniel Griscom May 12 '18 at 23:11
  • @DaveInCaz Thanks for the suggestion. There are few limitations here. FW tank has to be on the upper level roof because of washroom in the upper level and upper level roof tank cannot collect RW falling on the same roof. DanielGriscom, I'm from India. – Pavan Kumar May 13 '18 at 8:48

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