Although water butts are the simplest way to collect rainwater, a larger underground tank system can store enough water to meet your needs and prevents the false economy of using mains water as a back up.
The process is simple. Rain usually falls onto your roof, is channelled through the down pipes and then into the drain. Instead the rainwater is diverted into either a gully filter or an underground water filter. These remove large pieces of debris before the water falls into the underground water tank.