To provide a water supply/distribution system for performing an efficient operation with little energy loss, without using a large-scale farm pond and requiring an electromagnetic flowmeter to measure water supply amount and water distribution amount.

While a water storage tank water level detection means 8 detects an L level, a water supply/distribution control means 6 stops water distribution from a water distribution pipe 2 and drives a first water supply pump P1 or a second water supply pump P2 to raise the water level of a water storage tank 1 up to an H level. Based on time t required for the raise and water storage change amount ΔQ of the water storage tank 1 for the time t, discharge amount Qi per unit time of the first water supply pump P1 or the second water supply pump P2 is determined. Based on driving time for the first and second water supply pumps P1 and P2, water supply amount Qin to the water storage tank 1 is determined. Based on mass balance with total water distribution amount Qout derived from the water distribution pipe 2 for the time t, water distribution amount Qe to be distributed from the water distribution pipe 2 per unit time is determined.