I live in Mexico where we get city water two or three times a week which is stored in our small cistern. I want to add a second cistern and use the same pump for both to send water to the house. The two cisters cannot be connected at the bottom. How can I make this work?

  • Use a valve or valves to select which cistern you're drawing from?
    – keshlam
    Oct 4, 2015 at 20:03
  • 1
    Tell us more about the existing piping, cistern, and pump arrangement so we can better understand your question. What do you mean "The two cisterns cannot be connected at the bottom"? Can't you just run pipe from both cisterns to the pump suction, with one-way valves (check valves) to prevent flow from one cistern to the other? Oct 4, 2015 at 21:15
  • depending on the size of the present motor and existing plumbing you should be able to splice a "Tee" connector in the line and branch off to the second tank. I'm guessing that the cisterns are not high enough above the house since you need a pump? Would you prefer not having to manually open a valve when switching from one tank to the other? Is it possible to put the second tank on a higher elevation so as to make it gravity fed? Would it be feasible to construct a single, but larger cistern?
    – ojait
    Oct 4, 2015 at 22:37
  • The original cistern is below ground level under a parking pad, and a second, twice the size, would also have to be underground at the same level as the first cistern. Not possible to get to the first to connect them at the bottom of the tanks. The pump provides pressure for the house water system with no gravity assist, the pump does all the work. If I just put a tee in the pipes to add the second tank won't I lose suction if one tank runs out of water? If possible I would rather not have to manually switch between tanks, unless there no other answer. Oct 5, 2015 at 23:19

1 Answer 1


Put the second cistern above the first cistern, and let gravity move the water from the second into the first, leaving the pump on the first. Use a valve on the pipe from the second to the first to prevent overflowing the first when both are full/being filled.

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