Most treatments for coagulation now in vogue leave the water‐treatment operator with a potential pollution problem. The authors describe their laboratory work with the use of a coagulant that can be recycled and, moreover, that permits the operator greater latitude in “doctoring” the waters’ qualities in order to minimize potential corrosion problems. This is the first of two articles. Next month the JOURNAL will present the second installment, which will discuss the economic aspect.