Water Age Reduction in Distribution Systems

Public utilities are tasked with providing safe, potable water to the consuming public. Municipalities must take into account many factors when building the water distribution system. These variables require municipal officials to make projections about the future, and often, a lot of guesswork is required. To satisfy the different variables, the municipality must have a method of storage within the distribution system. Water is stored within this distribution system, either as part of a reservoir or within the pipe system, until needed by the consuming public. It is generally accepted that water quality degrades over time. Therefore, the longer water spends within the distribution system before it is consumed, the lower the quality. Disinfection by-products (DBPs) increase and residual disinfectant concentration decreases over time.

Water age is a function of water demand, system operation and system design. Demand can be irregular within a system, often varying significantly throughout a 24-hour period. Municipalities must also have sufficient flow and pressure within existing pipelines to satisfy customer demand and want. Many municipalities also must build new pipelines to handle the increased demand of a projected population 20 years into the future. Planning for projected population growth usually takes the form of a larger pipeline to handle the estimated increase in demand. Fire flow must be considered when designing and building the water distribution system. Fire flow is demand on top of regular consumer demand and must be achieved without taking away from the needs of the consuming public. Often, this extra demand requires municipal officials to consider investing in large storage capacity. The most significant distribution system impacts from fire flow requirements are adequate storage capacity and minimum pipe sizes.

Many utilities are turning to computer modeling to reduce water age in their distribution system. This modeling shows that reducing water age can be accomplished by several different methods, including increased tank turnover, variable speed pumps, reduced storage volume in low-demand zones, and elimination of dead ends. The use of modeling allows a utility to account for several variables at a time without facing actual consequences, like reduced fire protection.

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