12.1.1 Background

Until 1974, government regulators and water system operators concentrated their efforts on meeting water quality maximum contaminant levels (MCLs) at the water source or water treatment plant. However, with the implementation of the Safe Water Drinking Act in 1974 and amendments in 1986 and 1996, water system operators are being required to meet standards throughout their distribution systems and at the points of delivery. The Surface Water Drinking Rule requires that a detectable level of chlorine be maintained in the system. The Total Coliform Rule requires that total coliform standards be met at the customer s tap. The Lead and Copper Rule requires testing at the point of delivery (Clark 1994b; Clark et al. 1994, 1995; Pontius, 1996).

Water quality can undergo significant changes as the water travels through the water distribution system from the point of supply and/or treatment to the point of delivery. For example, chlorine concentration will decrease with time in pipes and tanks through bulk decay and through reaction with the pipe wall. Also, chlorine mass leaves the system at demand nodes or can be added to the system at chlorine booster nodes. Mixing of water from different sources can also affect water quality (Clark et al., 1995).

Pumps are usually...