About this calculator
Turn your daily water use and borehole yield test into the flow and head to give a pump supplier, plus the JoJo tank to store the water.
How it’s calculated
Flow = water needed per day ÷ the hours the pump may run. It must not be more than the sustainable yield on the borehole’s yield test certificate; over-pumping draws the water level down until the pump runs dry.
Total dynamic head = static water level + drawdown while pumping + height from the borehole to the tank inlet + friction loss in the pipe + any pressure needed at the outlet (1 bar is about 10.2 m). South African pump suppliers size borehole pumps from this head and the flow, reading the result off the pump’s performance curve. Storage is the daily use × the days of storage you want, rounded up to a JoJo vertical tank size.
Worked example
With these inputs:
- Water needed per day (litres)
- 1000
- Hours the pump may run per day
- 6
- Tested sustainable yield (litres per hour)
- 1500
- Static water level (m below ground)
- 40
- Drawdown while pumping (m)
- 10
- Height from borehole to tank inlet (m)
- 5
- Friction loss in the pipe (m, from pipe tables)
- 5
- Pressure needed at the outlet (bar, 0 for an open tank)
- 0
- Days of storage
- 1
the result is:
- Pump duty
- 167 L/h at 60 m head
- Flow
- 2.8 L/min (0.17 m³/h)
- Total dynamic head
- 40 + 10 + 5 + 5 = 60 m
- Share of tested yield
- 11%
- Hydraulic power (before pump losses)
- 27 W
Tips from the trade
- Use the yield test, not the driller’s first estimate; yields change with rainfall and neighbouring boreholes.
- A float switch in the tank and dry-run protection on the pump save the motor.
- Test the water quality before drinking it.
Common questions
What is total dynamic head on a borehole?
The total height the pump must lift the water plus losses: static water level, drawdown, the height to the tank, pipe friction and any outlet pressure. For water at 40 m with 10 m drawdown, a 5 m lift to the tank and 5 m of friction, it is 60 m.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and SANS 10400 (the National Building Regulations) and your local municipality before ordering.