Borehole pumps

A borehole pump is lowered into the casing below the water level and supplies the house from tens of metres down. It is chosen by three numbers: the dynamic water level, the borehole yield and the head the house needs.

• 3" — for narrow boreholes with casing from 80–90 mm;
• 4" — for 110–125 mm casing, the most common size.

The pump’s flow must not exceed the borehole yield, or it will drain the borehole and run dry. A worked example is in “How to choose a borehole pump”, and DIY installation in “How to install a borehole pump”.