At the greener homes exhibition I came across a company which install a water harvester system which is basically a giant 2000L drum placed underground in your back garden which collects & stores the rain water from the drains, this water is then used to supply toilets, dishwasher & washing machine, 2 problems with it tho, firstly it can only really be put into new-builds due to where it needs to be located and secondly at 3.5k it aint cheap, so I was just wondering if there is more of a DIY option!