I attended an interesting workshop this evening on rainwater harvesting, presented by John Caley, a sustainability consultant. This was organised as part of the Marrickville Council water tank rebate program.
A few notes from the evening:
- It makes sense to connect as many uses as possible to the tank, because that will leave more space for the rain to fill back up (greater usage can be more effective than a bigger tank).
- We get approximately 1,200mm of rain per year in East Sydney (3.3mm per day on average).
- Multiply out the square metre area of your roof by the 3mm/day figure to get an approximate figure for litres per day. In an ideal world, the household consumption would fit within that.
- Water usage from the hand basin and kitchen sink are not significant in the scheme of things.
- The best strategy is to increase the area of the roof that water is collected from, rather than increasing the tank size. This gives a much greater benefit for the effort (and cost).
In general, the workshop highlighted the value of working out:
- average amount of water that can be harvested per day from the roof
- expected household usage of water
- size of the tank to match
(Not that we did this, we just fit in the largest tank that was practical in the available space, and hoped for the best!)