We report a survey of the bacteriological quality of potable waters from hospitals. In the 12-month period February 1986 to January 1987, 646 samples were examined from 25 hospitals. Coliforms were isolated from eight (1·2%) samples, received from three hospitals. These hospitals did not, therefore, satisfy the European Community (EC) directive on potable water quality. Three hundred and four (47%) samples had total viable counts higher than the guidelines given in the EC directive on potable waters. Thirteen (52%) of hospitals surveyed submitted at least one unsatisfactory sample and six (24%) submitted more than 50% unsatisfactory samples. Water quality was generally poorer in the summer and autumn. Estimation of the total viable count is an inexpensive and simple method for monitoring the microbial quality of hospital waters.