TABLE OF CONTENTS Walter M.Grayman
Consulting Engineer
Cincinnati, OH
Lewis A.Rossman
U.S. Environmental Protection Agency
National Risk Management Research Laboratory
Cincinnati, OH
Edwin E.Geldreich
Consulting Microbiologist
Cincinnati, OH
The goal of a drinking water distribution system is to deliver sufficient quantities of water where and when it is needed at an acceptable level of quality. Although water quality may be acceptable when water leaves a treatment plant, transformations can occur as water travels through a distribution system. In the past, distribution systems were designed and operated mainly on the basis of hydraulic reliability and economics, with little attention paid to water-quality concerns except when serious problems arose. This attitude is changing as more water suppliers realize the important influence that time spent in a distribution system can have on water quality. This chapter reviews the most common processes affecting water quality impairment in distribution systems, methods for monitoring water-quality conditions and techniques for modeling water-quality transport and transformations.
The pipes and storage facilities of a distribution system constitute a complex network of uncontrolled chemical and biological reactors that can produce significant variations in water quality in both space and time. Factors leading to water quality deterioration in distribution systems include the following:
supply sources going on- and off-line,
contamination via cross-connections or from leaky pipe joints,
corrosion of iron pipes and dissolution of lead and copper from pipe walls,
loss of disinfectant residual in storage facilities with long residence times,
reactions of disinfectants with...
