In New Zealand many properties take their water supply from their own tank, which is filled by rainwater from the roof. No treatment is done, nor is it necessary. A simple diverter discards the first few minutes of rainfall (i.e. until the roof is "clean") and a grating deflects leaves and other debris.

Tank sizing at the beginning is very important, but if you don't get enough rain you can pay for a water tanker to show up (bit expensive though).

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