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Leaky distribution systems are costly in terms of lost water, potentially adverse water quality effects, and the energy consumed in supplying the leaks. To characterize the energy effectiveness of a leaky segment in a single pipe, several dimensionless parameters are analytically derived, which relate the leak size and location to its associated energy burden and water loss. The computer program EPANET is used to simulate the energy costs of leaks on representative distribution networks. In particular, analysis is performed to illustrate the influence of total system demand, leak location, and topological complexity. Furthermore, the connection between water loss and energy costs illustrates the potential importance of energy costs when pipes are leaky. The impact of leaks on water age is also evaluated through simulation and via a dimensionless expression relating leak size and location to residence time.

Given the rising concerns over scarce energy resources and global climate change, life-cycle inventories focusing on energy use and greenhouse gas ͑GHG͒ emissions were developed for the City of Toronto municipal water treatment system ͑WTS͒. Three processes within the facility use phase of the life cycle were considered: Chemical production, transportation of materials, and water treatment plant operation. The impacts of chemical manufacturing were estimated using the economic input-output life-cycle assessment model, while the inventories for transportation and operational environmental effects were based on data from the GHGenius model and regionally averaged data. Operational burdens, 60% of which are attributed to on-site pumping, accounted for 94% of total energy use and 90% of GHG emissions. By contrast, transportation-related energy use and emissions were deemed insignificant. The normalized energy use of the studied WTS was found to be between 2.3 and 2.5 MJ/ m 3 of water treated. Water conservation practices are recommended as abatement strategies for the energy use and GHG emissions associated with water treatment. The limitations and uncertainties introduced by selected model parameters and through combining various estimation methodologies are discussed, as is the model's relevance.

Transients can introduce large pressure forces and rapid fluid accelerations into a water distribution system. These disturbances may result in pump and device failures, system fatigue or pipe ruptures, and even the backflow/intrusion of dirty water. Many transient events can lead to water column separation, which can result in catastrophic pipeline failures. Thus, transient events cause health risks and can lead to increased leakage or decreased reliability. Transient flow simulation has become an essential requirement for ensuring safety and the safe operation of drinking water distribution systems. This article provides a basic understanding of the physical phenomena and context of transient conditions, presents practical guidelines for their suppression and control, and compares the formulation and computational performance of widely used hydraulic transient simulation schemes. Such capabilities greatly enhance the ability of water utilities to conceive and evaluate cost-effective and reliable water supply protection and management strategies and safeguard public health.A 112 MAY 2005 | JOURNAL AWWA • 97:5 | PEER-REVIEWED | BOULOS ET AL sient pressures are most important when the rate of flowis changed rapidly, such as resulting from rapid valve closures or pump stoppages. Such disturbances, whether caused by design or accident, may create traveling pressure and velocity waves of large magnitude. These transient pressures are superimposed on the steady-state conditions present in the line at the time the transient pressure occurs. The severity of transient pressures must be determined so that the water mains can be properly designed to withstand these additional loads. In fact, pipes are often characterized by their "pressure ratings" that define their mechanical strength and have a significant influence on their cost.

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