Fresh water production method

摘要

Provided is a fresh water production method applying a combined water-treatment technique employing a plurality of semi-permeable membrane units, the method enabling prevention of problems caused by growth of a biofilm and allowing effective use of an injected chemical agent and an injected neutralizing agent. The fresh-water production method produces fresh water by treatment of source water (A1) by a semi-permeable membrane treatment device (A2), the concentrated water (A) resulting from the treatment by the semi-permeable membrane treatment device (A2) is mixed with other source water (B4), and the water mixture is treated by a second semi-permeable membrane treatment device (B6). A first chemical agent is injected continuously or intermittently into the source water (A1) and a second chemical agent is injected continuously or intermittently into the source water (B4).