How do I work out the flow I need for my pond pump?

Knowing pond pump flow is critical for good pond pump choice – save money at the same time. Beware of maximum flow specifications on box

Be aware that pond pump flow is the amount of water required to give you the waterfall effect you desire in garden ponds and/or provide the bacteria in your pond bio filter with enough well oxygenated water to allow them to do their job of purifying pond water around the clock...

Correct specification of pond pump flow and pump head is very important. Too little flow and your waterfall will be a disappointment.

Too large a pond pump with too much water flow down a waterfall will waste your money and the noise may well annoy you and your neighbours too.

You must be able to determine the correct pump flow for your system in order to specify the correct pond pump. This is a MUST. By the way ribbed hose pipe is by far the best pipe to use on a garden pond since it does not restrict pump flow when bent to form curves or bends often required in a pond set-up.

How to measure water flow for an intended waterfall using a garden hose pipe

There are 2 basic ways and both involve a bit of calculation. One technique uses a hose pipe attached to the garden tap. here's the procedure for this method of water flow calculation ...

If you would like to test how much water looks best for your waterfall do the following ...

Place a hosepipe into the waterfall inlet
Adjust the flow until you are happy with the effect
Without closing the hose fill a known volume container from the hose pipe
Calculate the flow rate by dividing the volume of the container by the time taken to fill it. This week's free calculator could come in useful here.
This calculator would also allow you to weigh the container as an alternative to knowing its volume. For water use the following:
1 US gallon weighs 8.83 lbs
1 Imperial gallon weighs 10 lbs
1 litre weighs 2.2 lbs
If one hose does not deliver sufficient water then use 2 hose pipes.

How to calculate waterfall pump flow rate required using width of the waterfall overflow (lip)

A typical waterfall cascades over at least one edge. I will refer to this edge as the lip of the waterfall ... it is how wide this lip is that determines the flow required for a soothing waterfall sound. Of course you can have more or less water flowing down the waterfall but this is a good starting point to decide how much water you want to flow from your pond pump.

If your waterfall does not have a simple or single edge or lip then you must approximate. For example lets say there are 3 different overflow points and each one is 3 inches wide. Then use a total width of 3 x 3 inches = 9 inches.

For each inch of lip width allow for the following pond pump flow rates per hour ...

63 US gallons per hour for every inch (2.5 cm)

55 Imperial (UK) gallons per hour for every inch (2.5 cm)

250 litres per hour for every inch (2.5 cm)

Tip to improve appearance of waterfall without buying a larger pond pump

An under-powered waterfall is always disappointing. To make your waterfall look and sound better without buying a new pond waterfall pump do the following ...

Place some nice looking river pebbles at various points close to the overflow point(s). This has the effect of reducing the width of the lip over which the water from the pond pump must flow.

How to decide upon pond pump flow required if you do not have a waterfall

If you have a fish pond with no waterfall the pond pump flow is determined mainly by the pond bio filter requirements for oxygenated pond water. You will remember that every fish pond needs a biofilter and that it is bacteria inside the bio filter that keep the pond water clean and health for the fish.

To simplify the pond pump flow for this situation it is good enough to use the pond volume as the starting point ... yes this means you need to have a good idea of your pond's volume. If you click this link it will show you how to calculate the pond volume.

Most pond filter systems are satisfied by using a pond pump that will pump the volume of the pond through the filter between 8 and 12 times per day or put another way by using a pond pump that will pump the pond volume between every 2 or 3 hours.

So if your pond has a volume of 900 gallons then a pump that will deliver between 300 and 450 gallons per hour is good enough.

Now you know how to calculate pond pump flow and pond pump head lets show you how to use a pump curve ... click here how to read a pond pump curve

In addition to pump head and to fully specify a pond pump you need to know exactly what pump flow is needed for your garden pond.

When you see maximum pump flow referred to on a pump box do not use this for any practical purpose.

The information on many pond pump boxes must be treated with some caution. Good pond pumps suppliers clearly state volume flow at different heads. If you only see maximum pump flow stated on the box BE CAREFUL since the pump is only able to pump this amount with no pipe attached to it. Maximum flow is an impractical indication of true usefulness of a pump.

Think of pond pumps flow as the amount of water to be pumped around your pond system to give you a waterfall effect you will be happy with.

In addition pump flow must also satisfy the needs of your biofiltration system.

To save lots of money think of running two separate pond pumps in any pond with a waterfall – big or small pond, it does not matter. This subject is covered extensively in my book and this advice alone covers the cost of the book many times over.

In order to fully specify a pond pump you need to know in addition to pump flow exactly what pump head is needed for your garden pond.