How to Choose a Pump

How to choose a Pump


When considering the pump you might need, you need to try to work out what your water demand will be.

You will count the number of taps, water using appliances, irrigation and any other water use that might be used at any one time.  This will determine the total litres per minute you might need. 

We work on the basis that one tap is equivalent to 10 litres per minute. Consider that a normal shower is approx 10 litres per minute (LPM), although a rain shower head can be 14 litres per minute. A toilet flush is usually only 7LPM, and a dishwasher or washing machine might only be 4LPM and running intermittently. So we just take an average, and call it 10LPM per tap, which then allows for a bit more capacity.

This is only a guideline as to what size pump you may need, and there are other factors to take into account.

You need to consider other factors such as distance from water source to the house, elevation, pipe size and bends in the pipe system, all of which will create what is known as system friction and head loss.  If we are losing you here, please contact us for help, and have this information ready to discuss with us.

Generally, for the following size houses you will use:

Small Cottage or Bach:  1 bathroom - 1-2 taps

15-20 litres per minute

Small Home:  1 bathroom, single storey - 2+ taps

30-40 litres per minute

 Medium Home:  1-2 bathrooms, single storey - 3-4 taps

40-50 litres per minute

Larger Home:  2 bathrooms, 2 storey - 4+ taps

50-70 litres per minute

Large Home:  2+ bathrooms, 2 storey, multiple applicances - 5+ taps

70-110 litres per minute

 Very Large Building:  Multiple bathrooms, appliances and levels - 6+ taps

90-250 litres per minute

Pressure (Head):

Now to calculate what pressure (also known as head) you need. On a pump graph the vertical axis is measured in metres, and this is "head".  It represents the pressure a pump will deliver the water at (shown on the horizontal axis in litres per minute).

1m of head pressure equates to 1.42 PSI.  Most high pressure systems are 50-65 PSI and low pressure systems are around 40 PSI.

A pump does not pump at maximum head, nor maximum flow.  The optimum performance of the pump is in the middle and approx 25% either side of the middle of the curve.

So for example, having determined for example you need 30 LPM, and knowing you have a low pressure system (40 PSI), then you would select the pump with the top curve on the graph. 

However, you also need to consider distance from the water source (ie tank) to where the pump is situated, whether the pump has to suck water up, then the distance it has to pump the water to the furtherest point of use, whether your house is 1 or 2 stories, and pipe diameter. This is called friction loss, and if not factored in, will reduce pressure at the tap, so needs to be allowed for. 

We can help you calculate this, so just contact us on 09 294 7555 or email us on including as much of the info above as possible.