PRODUCTION OF DOMESTIC WATER

PURPOSE:To inexpensively produce a large amt. of drinking water contg. appropriate minerals and freed of nitrate ion by combining a reverse-osmosis membrane method and an electrodialysis method and specifying the nitrate ion content and conductivity of the mixed water. CONSTITUTION:The water drawn up from a well is transiently stored in a tank 2 and then pretreated 3, and a part of the water is supplied to an electrodialysis tank 4 to remove sulfate ion and stored in a mixing tank 5. Meanwhile, the desalted water from a reverse-osmosis device 6 is also supplied to the tank 5. The nitrate ion content of the mixed water in the tank 5 is monitored and controlled to =50mum by the feedback control of the electrodialysis tank 4 or reverse-osmosis device 6, and is operated so as to obtain the maximum amt. of produced water.