How to buy the best pump for your rainwater tank
A guide to flow rates, pressure, outlets and installation.
Making your water work harder
If you've installed a rainwater tank or you're shopping around for one, well done – you're doing your bit to help the environment. But catching the water is only half the battle. Now you have to send the precious drops around the house, and for that you need a water pump.
The first step is to decide what you want your pump to do, as this will determine how powerful the pump will need to be as well as any extra features the pump will need to direct the water where you want it to go.
A good flow rate (in litres of water per minute) will not only help you water your garden quickly – it's also an important factor in getting your flow to work at a reasonable level throughout the home. A good domestic pump should deliver at least 20L a minute which is around the same rate as a typical domestic town water tap; but most can manage more than this. The more water outlets the pump needs to service, the greater its maximum flow rate needs to be.
Water pressure from the pump is also an important factor – even more so if you're using the pump to power your domestic water supply rather than simply watering the garden. (Nobody likes a dribbly shower!)
What to look for
Pumps that turn on and off automatically when you turn on the tap (or hose) are easiest to use. You'll need this type of pump if you're connecting to indoor plumbing. Other pumps must be switched on or off manually, which may not seem to be a big deal but gets tiresome after a while.
Inside or outside pump options
Submersible pumps are generally quieter than external pumps, as the water in the tank muffles their noise.
This feature prevents damage to your pump's motor if the rainwater tank is empty (an important feature in drought-affected regions).
Prepare before purchasing
You'll need a weatherproof power point for the pump. If there's none close to its location, have one installed by an electrician. Don't connect the pump via an extension cord to an indoor power point, as this might not be weatherproof and could be unsafe.
Before you walk out of the store, make sure you have all the necessary fittings and hoses to connect the pump to a water tank. Don't assume these connections are all in the box – generally all you get is the pump. The supplier should be able to recommend the right fittings.
Most pumps are easy to install. External pumps should require a short piece of kink-resistant hose, secured with two hose clamps to connect the pump inlet to the rainwater tank. The distance between tank and pump should be as short as possible. Next, prime the pump with water, plug the pump into the power and switch it on. Ideally, you should put a housing or cover over an external pump to protect it from the weather and muffle its noise.
To install a submersible pump, simply connect the outlet to your garden hose, then lower the pump into the tank and plug it into the power supply. Make sure you don't use the power cord to lower or raise the pump.
If the pump is going to supply water to more than just a garden hose – for example, to your laundry or toilet – then you'll need more complex plumbing and controls and probably a more powerful pump too. Talk to a plumber or rainwater tank installer for advice.