rainwater harvesters

One thing the previous owners of the property thought about doing one day but had not done was to install a rainwater harvesting system. They were aware but did not get around to it. When they showed us the eight years of rainfall recordss, we thought that it should be a priority to install such a system.
Anywhere in the world with a similar annual rainfall, 600 to 700 mm, people would be doing everything to collect every drop from the sky. But here, there appears to be a complete lack of a rainwater collection culture. We know only two households collecting rainwater. Our plumber had never heard of a first flush diverter. When we talk to the locals about the neccessity of collecting rainwater, their typical reaction is "is it worth collecting when we have so little?" They seem to be quite content with the water scheme coming from the mighty rivers flowing from the Southern Alps.

The potential amount of water you can collect from your roof can be worked out as follows. One mm of rain on an area of one m2 makes one litre or roof area (m2) x annual rainfall (mm) = potential catchment (litre).

In our case, the roof is about 70 m2 and the annual rainfall last year was 790 in 2006 and 630 in 2007, or just below 700 mm in eight years, so the amount of water we can collect from our house is about 49,000 litres a year. We don't need a tank to hold this amount as we use as we collect. In our case we use about 150 litres a day (ie 54,750 litres a year), so we put another tank to collect water from the shed roof. The shed roof is about 40 m2, and should be able to catch an additional 28,000 litres a year. We may just break even.

In any case, the fact that we don't need to rely totally on a big water scheme for such an essential element of our existence means we feel more independent now.