Desalination system

There is provided a desalination system capable of monitoring a situation of a semipermeable membrane element in real time. 5 A desalination system 15 includes a plurality of semipermeable membrane elements 10 accommodated in series in apressurevessel1 2 , afirst intakeport 22 for intake of filtrate water from an upstream semipermeable membrane element 10in the pressurevessel 12, asecondintakeport26 for intake of filtrate 10 water from a downstream semipermeable membrane element 10 in the pressure vessel 12, and a supervisory controller 18 that outputs an index correlated with fouling on the semipermeable membrane element 10 based on at least one of first water quantity 46, first water quality 48, secondwater quantity 52, and second 15 water quality 54, the first water quantity46 and first water quality 48 being quantity and quality of the filtrate water from the first intake port 22 , and the second water quantity 52 and second water quality 54 being quantity and quality of the filtrate water from the second intake port 26. 5 - 23