The answer to you question depends on the particular conditions (e.g., temperature, etc.) of your application and what impurities in the water are causing it to be corrosive. It may turn out that you would be better off considering a more resistant material of construction for this application or then again, a coating may be acceptable. If you wish to pursue a coating for corrosion protection you should contact a manufacturer specializing in corrosion-resistant coatings for advice.