# can I fill a water tank from bottom?

I'm about to place a water storing tank at ground level and connect the water feeder pipe at the bottom of the tank. Would water fill normally as the top filling? Would atmospheric pressure + water mass pressure cause water feed pipe to stop following water?

• It would only fill until the pressure of the water column in the tank was equal to the pressure of the feed pipe. Commented Nov 25, 2016 at 14:33
• Is this tank outside? What is the volume of this tank and will it be pressurized by a pump? Where is the outflow to be located? Is this potable water or water for irrigation? Commented Nov 25, 2016 at 17:09
• @JimStewart Yes. This would be placed outside. Tank volume would be 500 Litres. And nope, water will not pressurized by a pump. It would be just an outlet from the city water supply, which in my area is less pressure. That's the soled purpose of having this ground tank. Commented Nov 28, 2016 at 7:49
• @Comintern Is there anyway to measure the column pressure? My feed pipe is 0.5 inch in diameter. Commented Nov 28, 2016 at 7:50
• If the pressure is enough to fill the tank from the bottom, it is also enough to feed it from the top. Either way, you need to get water to the height of the tank. If normal pressure can deliver water to the upper floors of a house, it ought to be able to reach the top of a tank at ground level. Commented May 5, 2017 at 7:34

If the pressure in the supply water line can force water up the outside of the tank and over the top, above the tank water level, then that same pressure can do what you want: force the water directly into the bottom of the tank against the same pressure head.

The problem is that, by making the direct connection at the bottom of the tank, you have no way of preventing a backflow of water from the tank, if the supply pressure drops below the pressure in the tank. If this backflow is into a city water supply, then this is a major safety hazard, and forbidden by most codes...

• A check valve would solve that problem. Commented Nov 25, 2016 at 23:23
• @DJohnM I was trying to make it bottom fill due to the water pressure is very low. I was thinking either I have to keep the tank ground level and fill from the bottom or bury the tank underground and fill from top. So as per your answer the later method seems correct I guess. Commented Nov 28, 2016 at 8:00
• @inckka: Would buying a pump not be much easier and cheaper than digging a huge hole? Commented Jan 12, 2022 at 11:33

Yes you can. Feeding the tank from above will exert the constant maximum head on the pump until the tank is full. Feeding from bottom leads to uniform increase of head from zero to maximum head. Also, feeding from the bottom will cut the energy consumption and time by half if the same capacity pump is used (I think). You can prevent the backflow by putting a NRV in line.

• My initial purpose was to connect urban water supply feed (which is very low pressure) to the tank and I wondered, since the water pressure is very low but constant in the ground level, either feed it to bottom of the tank or bury the tank underground and feed it from top. Anyhow as per the answers it seems both methods are same and I'd need to use a pump to get some pressure. However the NRV is a new thing for me. Thanks for mentioning that. Commented Jul 6, 2017 at 2:16

Top fill means that if you use a pump, the energy needed has to overcome the static lift and riser pipe friction. This does not happen with bottom fill, in which the only issue has to do with the pump curve [a plot of pump output against head] and at what point on the curve best efficiency is obtained. Assuming best efficiency when the tank is full i.e. at maximum head, then at low tank level, pump output and energy use are high, both dropping off as tank level rises, but efficiency is low and rises with tank level. if the pump was selected to perform best when the tank was one-half full, efficiency would rise to a maximum at half-tank then fall. Taking all of this into consideration, if you use pump with bottom fill, fill rate is not constant and slows with level rise and will probably take longer. With the top fill pump, fill rate is constant and a pump can be selected to provide best efficiency for a specific flow and easily defined losses.

• I should have added: If the water is coming directly from the public supply i.e. not via your own pump, then top fill is easier and cheaper. With any method, bottom or top fill, public supply pressure or self-owned pump you will need a (float) valve/switch to shut off supply to prevent overflow. With top fill this is all that is needed. With bottom fill, pumped or not, a check valve is necessary to prevent backflow into the public supply - something that water utilities hate. Commented Jan 12, 2022 at 14:00