The aluminum ion can inhibit the rusting of iron in water of pH 4. 1-4.5. Inhibition is achieved by using aluminum nitrate, chloride or sulphate (nitrate is best, sulphate the least good) at a concentration of 10-20 ppm. The addition of aluminum salt adjusts the pH to the required range, and the concentration is not very critical, though too low a value causes accelerated corrosion. The inhibitor is effective in stagnant and moving water. Inhibition is likely due to the formation of a thin hydrous aluminum oxide film, which insulates the iron from the solution. -- AATA