A water treatment system which comprises a reverse osmosis device having a fluid inlet, a permeate outlet and a concentrate outlet with a pump to pump a fluid through the reverse osmosis device, and a magnetic treatment device situated upstream of the fluid inlet, and filter means arranged to filter fluid from the concentrate outlet prior to recycling the fluid upstream of the magnetic treatment device. When a plurality of passes, the system reduces membrane fouling as the crystal structure of the precipitate is changed to reduce the amount of calcite to a deposit which precipitates mostly as aragonite.