All the toilets in our office are now equipped with water saving devices called Hippos. Fitting a hippo in larger cisterns can save up to 3 litres per flush! This can save you 5,694 litres a year. As we have 2 large cisterns fitted with hippos, we save approximately 11,388 litres of water per year. You can get them for free from Thames Water at http://waterwise.fortune-cookie.com/hippo-hotline/
What is a Hippo?

Hippo
A Hippo is a small plastic bag which can easily be fitted into your toilet cistern. Water is retained in the bag, helping to save water every time you flush.


Thanks for your comment Grazzer - I agree and if I lived alone would flush rarely but as I live with flatmates who are more sensitive and less environmental, the hippo is the best option for our diverse household :O)