Water treatment method and a water treatment system

The present invention can provide a high water recovery and treatment system that the water treatment method comprising salt water regeneration. The water treatment system of the present invention comprises: a first desalination unit, which comprises a Ca ion, SO4 ions and carbonate ions are separated into treated water of Ca ion, and carbonate ion concentrated water SO4 ions is treated with concentrated water; crystallization unit , which is disposed on the downstream side of the first portion of desalination, and having a gypsum crystallization from the first crystallization tank was concentrated water (21) and the first crystallization vessel (21) a seed supply portion supplying gypsum seed (22); a first pH measuring section (543), which was measured for the pH of the first concentrate in the first crystallization vessel (21); and a control unit (24), the pH measured by the first portion (543) measured by the pH scale in preventing calcium scale inhibitor is a case where the function to reduce the pH range, the control unit supply amount of the gypsum seed crystal is lowered by the first pH measuring section (543 ) measured by the pH than at high pH range, the control unit supply amount of the gypsum seed crystal increases.