Abstract: An object of the invention is to provide a method for preventing scale deposition that can prevent deposition of calcium fluoride scale without increasing phosphorus concentration in a fluorine-containing water system. Provided is a method for preventing scale deposition comprising adding a phosphorus-free maleic acid/ethyl acrylate/vinyl acetate copolymer to a fluorine-containing water system. The phosphorus-free copolymer is preferably a polymer obtained by copolymerization of monomer components containing maleic acid at a rate of 60 mol % or more, ethyl acrylate, and vinyl acetate. It preferably has a weight-average molecular weight of 500 to 5000.

Abstract: Provided are a water-treating agent which includes a specific nonionic polymer and a phosphorus compound and can exhibit the ability to inhibit the deposition of silica-based scale under wide ranges of water quality conditions and temperature conditions; and a method of treating water. The inhibitor for silica-based scale includes a nonionic polymer and a phosphorus compound, the nonionic polymer being: a polymer formed by the reaction of an unsaturated double bond and including units derived from at least one monomer selected from the group consisting of (meth)acrylamide, N-substituted (meth)acrylamide and N-vinyl lactam; and/or one or more polymers having an ether group and selected from the group consisting of alkyl alcohol/polyalkylene oxide adducts, aliphatic monocarboxylic acid/polyalkylene oxide adducts, and polyvinyl alcohol/polyalkylene oxide adducts.

Abstract: Provided are a water-treating agent which includes a specific nonionic polymer and a phosphorus compound and can exhibit the ability to inhibit the deposition of silica-based scale under wide ranges of water quality conditions and temperature conditions; and a method of treating water. The inhibitor for silica-based scale includes a nonionic polymer and a phosphorus compound, the nonionic polymer being: a polymer formed by the reaction of an unsaturated double bond and including units derived from at least one monomer selected from the group consisting of (meth)acrylamide, N-substituted (meth)acrylamide and N-vinyl lactam; and/or one or more polymers having an ether group and selected from the group consisting of alkyl alcohol/polyalkylene oxide adducts, aliphatic monocarboxylic acid/polyalkylene oxide adducts, and polyvinyl alcohol/polyalkylene oxide adducts.