Alternative Water Sources and Proactive Maintenance Part 1: Consideration for Source Water Blending

All water is created equal, right? Wrong. As the population in Texas continues to boom, the demand for water continues to increase. With this increased demand and the resulting impacts with ground subsidence, alternative water sources are needed. Alternative water sources are great solutions, but they also pose new challenges. This 6-part article series will highlight some of the challenges with alternative water sources and proactive maintenance needed to maintain distribution systems. 

Water supply challenges have driven many utilities to consider alternative water sources, such as addition of surface water to historical groundwater systems. While new sources offer a solution to capacity issues, water quality issues must also be addressed. Three major considerations are internal pipe corrosion control, disinfection compatibility, and hydraulic disruption of inorganic deposits in piping. This is the introduction of a multi-part series on best practices to control source water blending. 

Internal corrosion of piping, especially inside private homes and buildings is affected by many factors. pH, temperature, conductivity, dissolved oxygen, and calcium carbonate can influence corrosion that can lead to structural failures, as well as leaching of regulated contaminants such as lead and copper. Systems that have historically used one source of water must factor in the changes in these parameters after the new source and existing source have blended. This is especially difficult in systems where blending occurs within the distribution system where it is uncontrolled, and monitoring is often not feasible. 

A system that is adding a new source of water must balance the disinfection process. Many surface waters require careful control of disinfection to avoid formation of regulated disinfection byproducts. One common tool is to use chloramines as a residual disinfectant (and sometimes as the primary disinfectant). If the existing disinfectant chemical is free chlorine, a compatibility issue with chloramines can result in nitrification and ensuing degradation of water quality. Conversion of free chlorine disinfectant to chloramines is a typical approach, but the possibility of nitrification must still be addressed. 

Changes in hydraulic flow patterns and velocity in a water distribution piping network through the introduction of a new source of water can lead to disruptions in water quality. While the location of the introduction of a new source can be controlled, care must be taken to control how the new water is introduced in the piping network. Uni-directional flushing is a method to control the direction of the introduced water, allowing small sections of the piping network to be flushed out, with a controlled overall direction of flow from one end of the system to the opposite end. 





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