We have had a water butt (jojo tanks in South Africa) with 2200l capacity since 2010. The water butt water is used mainly to water our vegetable garden.
Last year we received another water butt from Hillcrest Primary as part of sharing their first prize in the Omo competition.Together we now collect 4400l of water each time we have rain of just 30mm. Both these tanks feed of two huge roofs.
Our school is billed as a business for water consumption so you can imagine the saving. Municipal water is not used for the gardens any longer.