Does anyone have a rainwater tank for flushing the toilet?

[Bramshott]

This is something I'd really like to explore, because it seems madness to use drinking-grade water for flushing the loo. I'm sure I've seen people doing it on a programme, either by fixing a tank to the side of the house, or burying one in the garden, but I'd really like to know how easy / expensive it is, and if there are any downsides.

Anyone??

I don't know anything about it, but it sounds like a fantastic idea to me.

There is a leaflet on it from the Environment Agency here but they seem a bit ambivalent on their main page about the benefits. Clearly it's also much easier to do with a new-build, and you have to think an easy way to flip back over to the mains if there's no water in the rainwater tank [brain exploding with complicated sciency-and-logistical-type stuff emoticon]!