To remove slime, rust and iron lumps, which are deposited on or stuck to the inner wall of a pipe, in a shorter water-supply cut-off time with lesser consumption of electric power and water, irrespective of the pipe layout.

This method comprises: discharging water in a required cleaning section of each of a water lifting pipe 3, a rising water supply main pipe 8 and individual branch pipes 10 by allowing the water to fall or extruding the water with an ozone-containing gas from any of ozone feeders A1 and another ozone feeder A2 to replace the water by the ozone-containing gas; filling the pipe section with the ozone-containing gas under a high pressure; then maintaining the pipe section in that state filled with the high pressure ozone- containing gas, for a prescribed period of time, to convert deposited or stuck. matter on or to the inner wall of the pipe section into easily releasable oxides; and subsequently, passing water through the pipe section to release the oxides from the inner wall, to entrain the released oxides into the water and to discharge the oxides together with the water.