Rainwater Harvesting, Lesson No 2

By Michael Bowater

There are certain things about the concept of rainwater harvesting that can sometimes be taken for granted, especially if you've been familiar with the process for a while. This was certainly the case for me while talking to a neighbour about rainwater tanks.

One thing that I'd noticed over the last few years driving my car around Melbourne, Australia were the amount of houses that have Rainwater Tanks installed (and they're just the one's you can see from the street). Rainwater tanks really are popular these days. The other thing that I've noticed is that most of these rainwater tanks are only connected to one downpipe (downspout).

I'd often wondered how much rainwater these tanks actually harvested and I got my answer while talking to my neighbour. I knew he'd installed a rainwater tank about a year previously so I asked him if he was happy with it and if it harvested much rainwater. He replied that he wasn't, as we don't get enough rain to fill it. I told him that he needed to connect more of his roof area to it. That way he could harvest more of the rain that fell on his roof.

Talking to my neighbour though I realized that there were probably many other owners of rainwater tanks that also had the same misconception my neighbour had, which was ... you can't harvest very much rainwater if you're not getting very much rain.

I then went on to explain to my neighbour that because I can harvest rainwater from all of my roof area, I can in fact harvest lots of rainwater and that I use rainwater in my garden throughout summer and I've never run out of stored rainwater.

This is highlighted by the example of the roof on my house. My roof can now harvest 75,000 litres of rainwater per year from just 300mm (12 inches) of rainfall. That's enough to fill a 4,500 litre rainwater tank over 16 times over. But even better, the great thing about rainfall is that most climates don't get it all at once. That means you don't need a 75,000 litre rainwater tank to store that amount of rainwater.

So that was the second lesson I learnt about Rainwater Harvesting ... you don't need lots of Rain to Harvest lots of Rainwater.

The roof of your house is one of the best assets you have when harvesting rainwater. It's knowing how to harvest that rainwater that makes the difference. Even in times of low rainfall knowing the right rainwater harvesting techniques is very important.


I've been harvesting rainwater for my garden for the last three years and as a consequence have become quite adept in the process of rainwater harvesting.

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