Abstract: A fish farm having a land-based fish tank (1a-e) and a water supply system (100) with a supply line (2C,D) and a discharge line (2A,B) fluidly connected to a water reservoir (3); a fluid intermediate storage (5,6, 56); a circulation conduit (9a-f) fluidly connected to the fish tank (1a-e); a valve arrangement (10a-p) fluidly connected to the supply line (2C,D), the discharge line (2A,B), the fluid intermediate storage (5,6, 56) and the circulation conduit (9a-f), the valve arrangement (10a-p) having first and second operational configurations for circulation of fluid between the fluid intermediate storage (5,6, 56) and the tank (1a-e) via the circulation conduit (9a-f) and for circulation of fluid between the fluid intermediate storage (5,6, 56) and the reservoir (3) via the supply and discharge lines (2A-D). There is also provided a method for operating a fish farm having at least one land-based fish tank.