Two Italian laws, come into force in the 2003, prescribe the use of the Standard UNI EN 12780 for the determination of Pseudomonas aeruginosa in water. A shortcoming of this method is due to long time for obtaining the analytical results. In this paper the performance of an early warning method, the Colifast Analyzer/Pseudomonas aeruginosa, was evaluated, respect to the standard reference method and for its sensitivity, specificity and time to detect. The Colifast Analyzer/Pseudomonas aeruginosa gave different results according to the analyzed water and much quickly than the standard reference method. The system could have wide prospects in a future also in relation to an adaptation of water technical regulations.