# Impossable with a pump to suck water from a lake

## Main Question or Discussion Point

Hiya
my question is

Why is it impossable with a pump to suck water from a lake if you place the pump 15 meters above the water

I think it has somthing to do with gravity but if anyone could explain it in detail that would be great

Thanks :)

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Gold Member

Well yes the water is held down by gravity.

yes but i was thinking what stops me from making a pump so large the i can pump anyways

Pumps don't suck. They can only remove the air/water that is already in the line. Then the ambient air pressure pushes the water up. 14.7 psi = 33 feet of water= 10m of water.

Have you ever looked at a mercury barometer where the column of mercury is about 760 mm (millimeters) high, with vacuum above the column, and air pressure pushing from the bottom? There is no way that the suction (vacuum) can be made any better. Because the mercury density is 13.6 times higher than water, the absolute max column of water an ideal pump can suck is 760 mm x 13.6 = 10.34 meters (at sea level).