Enough rainwater can be harvested from an average house downpipe to supply a 3000L tank connected to the toilets and laundry. By ‘average’ we mean a downpipe from a gutter that’s collecting water off 30-40 sqm of roof. A downpipe off a narrow setback roof or a porch for example isn’t going to supply that much water and would be more suited to a smaller tank.


Installations designed to maximise the use of rainwater will be more effective taking water from two or more downpipes into a 5000-6000L tank. If the tank is supplying a hot water system then a decent catchment area is important to be able to refill the tank quickly during light rain (i.e. in normal conditions).


If you wish to harvest rainwater off the entire roof this is done by connecting all the downpipes to an underground collector that runs into the tank. This will work with a normal surface tank so long as the entry point to the tank is at least 300-400mm below the gutters. Installing a ‘wet’ or ‘charged’ system that works well is rather more complex than a simple pipe straight into the top of the tank – ask us for help.


Many people have an issue finding a space next to a downpipe that’s large enough for the size of water tank they need. There are several ways to solve this:

1.  Find another location for the tank  There is often more than one alternative, maybe using a different shape or size of tank
2.  Run the downpipe along the wall to a better spot  Inexpensive, but often looks messy, and won’t work on all homes
3. Move the tank away from the wall – against the fence for example Pipe can span across a path (much further than a metre and it’ll start to sag over time)
4. Run the pipe underground and then up into the tank Works well and distance is not a problem but the pipe does remain ‘charged’ or full of water and the system must be carefully designed.

For a large tank draining most or all of the house roof this is generally the only practical option

Did you know? Enough rain falls on the roof of an average Perth house roof to be self-sufficient in water – if only it could all be stored! 

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