One easy way to save water if you have an older WC toilet cistern that flushes nine litres or more is to add a small balloon filled with water, which ever will fit best. The cold water flush will be reduced by the volume of water in the balloon . You should place the balloon so that it does not get in the way of the movement of the ball valve float. Newer cisterns only flush six litres of water so adding a balloon or other water saving device is not beneficial and may cause you to use even more water, with repeated flushing necessary but many have dual flush buttons ;small button reduced flush; large button full flush.
Make sure the balloon used is of a good grade as a burst will over fill your cistern.
pluming advise by a local southport plumbing company march 2013