Gray water is recycled water that can be reused. There are many types of water collection, including rainwater harvesting and collecting the water from your showers and bathroom sinks. Rainwater harvesting is one of the more popular methods for water collection and involves collecting water from gutters using a cistern or other collection device; these come in sizes ranging from 50 gallons to 5,000 gallons or more. The collected water can be used for landscaping or in toilets.
Another technique is to use indoor tanks that collect water from showers and bathroom sinks. This water can be reused in toilets or for underground irrigation. Water from the kitchen sink or toilets should not be collected and stored because it contains bacteria.