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We are building our home (a 2-storey house) and a cistern tank was suggested by our architect for aesthetics. We asked around the neighborhood and one person has a cistern and an overhead tank but uses the cistern more on a daily basis while the overhead tank is used when there's no power. The ground floor is also connected directly to the city water line while the 2nd floor is pumped from the cistern due to low pressure up to the 2nd floor. The other neighbor only uses an overhead tank in their backyard.

We are quite concerned on aesthetics and safety but also about the cost of electricity if we use a cistern powered by a tank to supply the 2nd floor of the house. We were told by our architect that we can find an energy saving pump these days and in case there's no electricity, we can always buy a cheaper generator as back-up.

Also, our architect suggested we have a cistern to store rain water for use in gardening and supply water to the pond which we think is a great idea.

Are there other reasons for choosing a cistern tank vs an overhead tank?

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Do you know what the flow rate from your public water system is? Also, what height would the overhead tank be installed at? – pdd Sep 25 '12 at 1:22
  • A cistern tank is shielded from all elements-the temperature will be less volatile.
  • Sun warmth can not increase bio live.
  • They work for centuries now.
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  1. Economy: If you cannot get the water pressure to reach the 2nd floor, you have to pump it there. But if you build an overhead tank you'll have to pump to even higher altitude with a more powerful (read more expensive to buy and maintain) water pump. And you are going to use more energy to get it there although bigger pumps usually have better power efficiency.
    I'd use a water pump with a pressure vessel which can even overcome a short electricity shortage and can be very energy efficient.
    The cost to build an overhead tank itself seems to be higher than a cistern.

  2. Water quality: If the water is stored in higher temperatures than 25°C (77°F), the danger of legionella should be considered. That's why storing potable water in an overhead tank (exposed to sun heat) isn't a good idea.
    Storing the potable water in a back-up storage for longer periods isn't an good idea neither - it will become too stale. It could be used in the backyard or in the toilet but not in the kitchen.

  3. Freezing: You don't mention the location in your question. Is there any possibility of freezing in your area? Should you heat the overhead tank and the supply line in winter or empty it and not use it at all?
    The top of the cistern should be below the freezing depth to keep it operational and to prevent damage.

  4. Still there is one point against a cistern tank in favor of an overhead tank. If the level of underground water is too close to the ground level, it can spoil the stored water or displace the cistern.

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