Drinking water microbiology has emerged from decades of relative complacency to recognize there can be major concerns with potable water quality. Many of these issues are a result of an explosion of information on new waterborne agents, treatment problems with raw-source water qualities, biofilm development in some distribution systems and specialized requirements in water quality unique to hospitals and industries. Protozoan cyst survival after some disinfection practices involving surface water impoundments and virus occurrence in poorly protected groundwaters have provided reasons for expanding minimum treatment of surface waters and for requiring disinfection of all groundwaters unless there is a demonstrative data base to support exceptions in treatment requirements. Official monitoring of small water supplies must be increased on a monthly basis and a rapid alert established to inform water plant operators of unsatisfactory water qualities. As an option, application of operational tests to analyse water quality in terms of chlorine residual, turbidity, total coliforms and heterotrophic bacterial counts in small water plant operations should be encouraged. This would provide the operator at remote locations with the opportunity to utilize the information to make necessary treatment adjustments or corrections in water distribution deficiencies promptly and be a supplement to the official regional monitoring program. Application of drinking water alternative sources (bottled water and water from point-of-use treatment devices) should be viewed by the health authorities as only a temporary solution, not as a permanent fix for a public water supply known to present some established health risk to consumers. The public must also recognize that bottled water is not frequently monitored by health laboratories for acceptable quality and the use of home treatment devices places the responsibility of proper maintenance on the user. Microbial quality improvements in drinking water to hospitals and food industries can frequently be achieved through a routine, systematic flushing program for building plumbing networks and associated attachment devices. In other situations, use of booster disinfection or point-of-use devices may provide the important special water quality requirements for certain industrial applications. In any event, these supplemental treatment measures will require careful in-plant monitoring and maintenance to prevent reversals in water quality enhancement.