A tank used to hold cold water is usually known as a cistern. Cisterns today are made of black plastic rather than any older material. The use of plastic allows them to be light, durable and flexible which can make it easier to fit into the loft and they also resist the growth of any bacteria. Insulating the cistern can prevent the water freezing, but it also stops warming of the water from below. Installation of these type of cisterns can be carried out by professionals such as Ashford Plumbers .Locating of cistern. Modern plastic cisterns are flexible so the base must be fully supported. It is unacceptable to stand them spanning across joists without providing a solid platform between the two. The weight of water could distort the cistern with potentially disastrous consequences. The cistern’s outlets should be higher than any of the draw off points for fittings and appliances.Inlet (cistern).Water supply is controlled by a valve known as a ballcock or ball valve. This will most likely be a diaphragm valve rather than the older style valves. Diaphragm valves discharge water from the top and this allows a sufficient air gap to prevent backflow. This enables the cistern to be filled and shut off automatically according to the water level. Adjustment of the valve once it is fitted enables a specific maximum water level to be maintained.Outlet (cistern).The connection for the outlet from a cistern should close to the base or even underneath so that debris cannot accumulate. Both the Inlet and the outlet should have local shut off valves allowing isolation of the cistern. The inlet is usually a plug valve type. The outlet will normally be a regular gate valve.The Overflow.Has to be fitted over the maximum water level but below the inlet enough so as to maintain the required gap of air. The pipe runs downhill so that water flows freely down it and out through an outside wall. The pipe should be insulated and protected with a mesh screen to stop insects and dirt from entering the system. The pipe is 19mm (usually). If you have any doubts about your ability to carry out the work you can always call an expert like a local Ashford Plumber for advice and guaranteed work.