Hippo the Toilet Water Saver conserves about 3 litres of water each time a toilet is flushed. This is approximately 33% of water used in a toilet, and 10% of total water used in a house.
The Hippo is made from heavy gauge polyethylene, which sits in the toilet cistern. When the toilet is flushed, the water confined in the Hippo is saved. If you find the level of saving impairs the flushing, you can simply cut off one of the bottom corners of the bag.
Each Hippo has a small hole punched through both sides. This acts as a relief valve, allowing slow circulation of water to prevent stagnation and evaporation.