A cistern comprises an upper water tank as a first chamber, and a lower water tank as a second chamber connected by an opening. At the top of the upper tank a mains water inlet allows mains water into the tank through an inlet valve, which is under the control of an upper float. An auxiliary water inlet allows water from an auxiliary supply, such as condensate from an air-conditioning unit, into the tank. At the bottom of lower tank is an water outlet, which allows flushing water from the lower tank 104 to flush an appliance (not shown) under the control of an outlet valve. The outlet valve is under the control of an actuator, which is configured to move up and down, and is also under the control of a lower float.