Sudden valve closures can create rapid changes in water velocity that result in transient pressure conditions. Pressure transients can travel throughout a distribution system and cause low or negative pressures. Contamination may occur if a leak or air-vacuum valve is submerged and a low pressure wave passes through the pipeline. Pressure transients may be initiated by regular water distribution system operations. Therefore, pressure transients may occur frequently in certain water distribution systems. The objectives of this project were to verify that low and negative pressure transients actually occur in real distribution systems (not just within large transmission mains) and that they can cause contaminants external to the pipe to be intruded into a drinking water main through a leak or orifice. The research strategy for this project was divided into five primary tasks: (1) an expert panel workshop; (2) design and construction of a pilot-scale test rig and associated testing to measure intrusion volumes under various operating conditions; (3) field studies including pressure monitoring in seven full-scale distribution systems plus comparison of mechanical pen and chart recorders, data collected by SCADA systems, and high-speed data loggers; (4) evaluation of the capabilities of full-scale hydraulic surge modeling; and (5) development of a surge control program and control strategy guidelines.