At the moment, the SA government is offering rebates to get us onto rainwater tanks.
I'm interested - if I wanted to live off of rainwater, is it worth it?
25000L tank (3.4m diameter, 2.4m high, needs site leveling)
5000L tank (much smaller, can be stuck next to house)
Automatic or manual switch.
After crunching the numbers, it's pretty pathetic. My best bet is to fork out the $2359 for a 25000L tank and get it plumped into my house / site leveled, etc. Based on my current quarterly water usage ($34 actual water usage, the rest is sewerage and supply- ACK!); and assuming that I can get the tank filled from rain 4 times a year (unlikely!); it takes me 23.59 years to get my money back.
Given the roof size of my house and shedding, I wouldn't be able to fill 25000L four times a year.
You can play with the spreadsheet if you like.