Coliforms of the genus Klebsiella were found in many finished drinking water supplies which used reservoirs constructed from redwood. Coliform contamination was associated with slime which accumulated on some stave surfaces below the water line on the tank interior. Based on the results of field surveys, design modifications were made on an experimental 1,000 gallon reservoir in order to control coliform contamination. Coliforms were not found when free chlorine residuals of 0.3 to 0.4 ppm were maintained in the tank water. Poor water mixing and retention times of 7 days or longer made it difficult to maintain a free residual due to the chlorine demand of the wooden reservoir. Minimum retention times (less than 7 days) and adequate water mixing (no common inlet/outlet) can be achieved by proper choice of reservoir size and regulation of float levels. In the absence of free chlorine residuals, Klebsiella are able to multiply on water soluble nutrients leached from the redwood. Cyclitols, comprising 4.5% redwood dry weight, are the nutrients which uniquely support the growth of Klebsiella and Enterobacter in the redwood environment. Information in this report will be of interest to technically oriented personnel in water supply and treatment and environmental microbiologists.

Grant no. R804456. July 1979. Includes bibliographical references. Microfiche.