Abstract: Water-circulating systems are treated with an aqueous, alkaline composition comprising I) an organo-phosphorus chelating agent, II) an acrylate homopolymer, III) a salt of an acrylic copolymer, a portion of the repeating units of which contain sulfonate groups, IV) a molybdate salt, and V) a salt of a fused-ring aromatic triazole. This composition (which is formulated in accordance with a specific order of addition of the ingredients) is effective against white rust (corrosion of galvanized metal parts). When the water-circulating system is also fouled with a biofilm, it is preferred to introduce a biofilm remover having biocidal, surfactant, and chelating properties into the system, but the biofilm remover is introduced separately from the above-described composition.