Provided is a water treatment agent composition which is a one-part preparation comprising a hypobromite salt that acts as an inorganic slime control agent and an anti-corrosive agent, and in which the inorganic slime control agent is prevented from the significant deterioration in slime control performance thereof (i.e., the significant deterioration in oxidizing power thereof). A water treatment agent composition comprising a bromine-containing oxidizing agent or a reaction product of a bromine compound with a chlorine-containing oxidizing agent, a sulfamic acid compound, and at least one anti-corrosive agent selected from a polymer containing a monomer unit represented by formula (1), a polymer containing a monomer unit represented by formula (2), a binary copolymer containing a monomer unit represented by formula (1) and a monomer unit represented by formula (3), a ternary copolymer containing a monomer unit represented by formula (1), a monomer unit represented by formula (3) and a monomer unit represented by formula (4), a phosphino carboxylic acid copolymer represented by formula (5), a bis(poly-2-carboxylethyl)phosphinic acid represented by formula (6), a 2-phosphonobutane-1,2,4-tricarboxylic acid represented by formula (7) and salts thereof, and an azole compound, wherein the components are compounded at pH 13 or higher.La présente invention concerne une composition d'agent de traitement de l'eau qui est une préparation en une partie comprenant un sel d'hypobromite qui agit en tant qu'agent de contrôle des boues inorganiques et un agent anticorrosion, et dans laquelle l'agent de contrôle des boues inorganiques ne subit pas de détérioration significative dans sa performance de contrôle des boues (c'est-à-dire, de détérioration significative de son pouvoir oxydant). La présente invention décrit une composition d'agent de traitement de l'eau comprenant un agent d'oxydation contenant du brome ou un produit réactionnel d'un composé de brome avec un agent d'oxyda
