Abstract: Disclosed is a method for obtaining a tenacious insitu coating deposition of calcite on the inner surface of water pipes. The calcite coating method according to the present invention has an advantage that it is able to maintain a completely corrosion-free system during the coating, thus assisting the formation of a protective coating of good bonding properties. The method consists in the incorporation of a reagent selected from the group consisting of alkali metal sulfite and hydrazine, in an amount which is at least the stochimetrically required to deoxygenate the aqueous solution utilized for said coating, which is supersaturated with respect to calcium carbonate having a dissolved calcium and carbonate levels of above 100 ppm. The calcite producing ingredients are supplied to the water stream in quantities supplementing concentrations available in the natural water used, giving the required supersaturation levels by addition of suitable salts.