To sterilize cooling water for an air conditioner periodically by releasing water soluble liquid germicide or the saturated water solution of it inside a controlled release medicine cartridge to the city water that flows through distributing water pipes in the supply of the city water to a cooling tower.

The city water that flows into the controlled release medicine cartridge 2, proceeds towards the closed edge at the central part, diffuses radially and flows toward the opening edge of the controlled release medicine cartridge 2 as a cylindrical flow along the wall of the circumference of it. In the process of it, the germicide solves into the city water and the city water becomes the saturated solution of the germicide. The germicide solution flows out through the porous film 2a that covers the opening end of the controlled release medicine cartridge 2 to the outside and is mixed with the city water flowing by. The city water that is mixed with the saturated solution of the germicide flows into the supply distribution pipes 1 at the down flow of the bulged part 1a and then flows into the cooling tower. As the result of it, the germicide is added to the cooling water for the air conditioner periodically and sterilizes it.