A thermal expansion/surge reduction water tank includes a hollow housing with a bladder sealed to an inside of the housing forming two compartments therein. A compressed air inlet in communication with a first of the compartments is provided for expanding the first compartment by focusing the bladder into an abutting relationship with the housing inside. A water inlet and a water outlet in communication with a second of the compartments is provided and disposed for causing non-laminar flow of water through the second compartment for both expanding the second compartment by forcing said bladder into the first compartment and flushing the second compartment to effect self-cleaning thereof. A plurality of protuberances disposed on a side of said bladder facing the second compartment are provided for preventing sealing of the bladder in an area of abutment with the housing inside between the water inlet and outlet thereby enabling fluid flow between the water inlet and outlet with said bladder abutting the housing inside.