Especially in developing countries, the problem of adequate drinking water supply is an ever growing one. Public health programmes have been established to improve the population's health conditions, but these programmes require big financial means for guaranteeing adequate supply of potable water and medical therapy for sick people. Too little emphasis is still put on regular testing of drinking water for microorganisms such as Aeromonas sp. and Vibrio sp. In a spot check analysis in various countries, the importance of Aeromonas sp. is shown--not a single sample complied with international norms and guidelines for drinking water.