The condensate water discharged from the compressed air installations contains a series of contaminants such as solid particles and oil which, if not properly removed, contribute to seriously polluting the environment. The recent European directive 91/271 /EEC concerning the treatment of waste water and 91/676 /EEC concerning the protection of water against pollution caused by nitrates, clearly indicate the maximum concentration of oil allowed in the condensate discharged without violating the law. This water /oil separator, thanks to a patented 2-stage filtration system, absorbs the residual amount of contaminants without the need for complicated sizing formulas.