The heat preservation water tank means adding special industrial and thermal insulation materials to the interlayer of the water tank, so that the water tank will maintain a certain temperature to meet the needs of life or industry. The thermal insulation water tank can be divided into: the stainless steel insulation water tank under the pressure and the insulation water tank glass steel insulation water tank. The thermal insulation water tank is divided into the shape of the cylindrical heat insulation water tank and the module splicing water tank. The cylinder water tank usually can be done 1-12 tons, and the large volume can be used for modular splicing water tank. The modular splicing water tank is made up of 1M*1M and 1m*0.5m stainless steel plates. It is composed of three parts: a high water tank, a storage tank and a low water tank. The water tank is provided with high mechanical control device, run water flushing valve and drain valve, float electrode switch, run water heater and flush valve seat are respectively arranged in the storage tank and the three water pipes connected, open drain valve, high water tank is communicated with the water storage tank; the water tank is provided with low lever type float switch, float the valve opening, the water storage tank is communicated with the lower water tank; low water tank is also provided with a submersible pump, filter and drain pipe, water outlet pipe of the submersible pump in high water tank, close the control electrode through high water tank float switch for submersible pump. The use of the medium water tank can save a large amount of clean water for drinking, with significant social and economic benefits. The medium water tank can be used with the existing various types of stool. It can be used in hotels, restaurants and enterprises and institutions with large amount of water.