Gravity Flow Tanks

A gravity flow tank, where possible, is the best domestic water supply. Water is pumped to, and flows back from, a large tank uphill from the house. The tank should be at least 22 feet higher than the point of use, to get 10 pounds or more water pressure (2.3 feet elevation per pound of pressure). It should be buried to keep cool and avoid freezing. There was no hill above us to site a tank so we put four 100 gallon tanks at the highest heated level (4th floor) of our tall house. Pressure is only 7 pounds at our 2nd floor kitchen, but with 3/4″ and larger pipes, and no small restrictive couplings to the faucets, we get good flow and fine showers on the 1st and 2nd floors. NOTE: Instant (tankless) gas water heaters require at least 12 to 15 pounds of pressure to operate properly.

Pressure Tanks

A pressure tank stores pressurized water without an uphill or elevated tank. A pump pushes water into the tank and that compresses captive air in the tank. The air provides continuous pressure for water delivery. The pump recharges water to the pressure tank as needed. Since pressure tanks are small, they need refilling often. An inverter powered 110 volt AC deep well pump or DC powered surface pump can refill the tank as frequently as needed. Pressure tanks in sizes from 20 to over 80 gallons are sold at hardware and plumbing stores.

Larger Water Storage

What if your AC pump must be high powered and 240 volt so it can run only on generator power? A larger water storage tank is needed so you can start the generator only once a day or once a week to refill it, rather than starting it each time water is used. Large volume water storage, when no uphill tank is possible, can be done two ways:

• Use several pressure tanks, enough for a day’s water from one filling.
• Use a large buried tank near the house (or on a tower in non-freezing climates). This tank is filled by the well pump once a week or less often, using either a slow DC or fast AC pump. A second DC powered pump uses this tank to refill a small pressure tank in the house as often as needed as you use water. This eliminates starting an AC pump often, or waiting for a slow DC submersible well pump to refill the pressure tank.

NOTE: DC diaphragm pumps should never push water directly to your faucet without a pressure storage tank. It works, but more energy is used, and the pump and switch wear out quickly. Our EZ-SET-UP kit accessory includes instructions for both plumbing and electrical connection of DC pumps with pressure tank.

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