Optimum water volume during drafting from a source is achieved when the water surface is located how many meters below the pump?

• A. 1 meter below
• B. 3 meters below
• C. At the surface
• D. 5 meters below

Answer: (B)

In drafting from a water source, the pump must create suction to lift water up to the pump. The amount of suction head the pump has to overcome depends on how far the water surface sits below the pump. A depth of about 3 meters below the pump gives a stable, manageable water column in the suction line. This depth helps keep the pump primed and minimizes air entrainment at the intake, while not demanding excessive suction that could lead to cavitation or loss of prime. If the surface is too shallow, turbulence and surface air can cause air pockets entering the suction line; if it’s too deep, the pump would have to lift a larger column of water, increasing friction losses and the risk of losing prime. Therefore, 3 meters below the pump is considered the optimal depth.