Piston type water tank

The invention relates to a piston type water tank and belongs to the technical field of household appliances. The water tank is partitioned into two isolated spaces through a piston, heated hot water is isolated with and not mixed with newly fed cold water, and relative stability of water temperature is guaranteed. When the piston type water tank is used, a water inlet valve on one side (end A) of the heated hot water is closed, and a water outlet valve is opened; a water inlet valve of the other side (end B) of the heated hot water is opened, the water outlet valve is closed, the B-end inlet water pressure pushes the piston to move towards the A-end hot water (water outlet) side, and the hot water is pressed out. After the hot water is emptied, the A-end water inlet valve is opened, the water outlet valve is closed, cold water enters the tank, the hot water is pushed by the piston to be discharged out of the water outlet valve, the operation is conducted repeatedly, and constant water temperature is achieved. Compared with the prior art, no external power is needed, energy is saved, the size is small, and the cost is lower due to the pure mechanical structure.