Leveraging the existing Rainwater Butt

I looked at my standard rainwater butt. It's connected to the main house roof drainage. As before, some calculations:
  • Rainfall about 0.72m/year
  • Effective roof collection area about 27m²
  • 0.72 x 27 = 19.44m³
  • About 20,000 Liters 
  • 4,000 watering cans 
  • Butt capacity 200L
  • Can fill the butt 20,000/200 = 100 times.
In practice, the overflow/diverter device throws away over 90% !!
Some preliminary ideas:
  • It might be worth getting a larger or supplementary butt to help cope with prolonged drought.
  • On the other hand, using a watering can is quite a chore already
  • Might a more automated system be possible?
My existing butt fills up to about 150mm above the inlet from the overflow/diverter. On the other side of the butt, there's scope for another pipe. I decided to make this an outlet to the garden.


  • The butt has to fill up to the new outlet before any extra water goes to the garden
  • The next 30L goes to the garden
  • Heavy bursts of rain may still be wasted by the overflow/diverter

Clearly, this supplementary watering system isn't a complete solution to all my irrigation problems.

 Strengths
  • Useful source of water for crops under cloches
  • Useful for dry spots caused by trees/walls
  • Good for plants that can use extra water but are not dependent on it
Weaknesses
  • Doesn't help with drought
  • Uneven supply of irrigation - some food crops don't like this
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