The Domestic Envireau Rainwater Harvesting system has been designed as a low cost installation for self-build projects and residential developments. BBA certified, it works by taking the rain from your roof gutters, filtering out the leaves and debris and storing the water in an underground tank. This is then pumped into the house to be used for non-potable applications such as toilet flushing and washing machines. If the tank runs empty, the system automatically switches to mains supply. Simple.