Water Operations Division

The Multi-Barrier Approach to Safe Drinking Water

The key to ensuring clean, safe and reliable drinking water is to understand the drinking water supply from the source all the way to the consumer's tap. This knowledge includes understanding the general characteristics of the water and the land surrounding the water source, as well as mapping all the real and potential threats to the water quality. CWD commissioned a report by the U.S.G.S -Report 00-4262, which details Source-Water Protection published in 2001. This report assesses the factors affecting reservoir and stream water quality in the source area. In addition CWD brought online in 2001 a state-of-the-art treatment plant. CWD has implemented many upgrades to the distribution system to safeguard against operational breakdowns and aging infrastructure. The multi-barrier approach makes sure there are "barriers" in place to either eliminate potential threats or minimize their impact. To safeguard this precious resource CWD has implemented a dynamic Watershed Protection Plan, the use of effective water treatment and proactive management of the distribution system.

Process Description

The Cambridge WTP employs Pretreatment with Fresh Pond Aeration, Preoxidation, and Dissolved Air Floatation (DAF), Primary Disinfection with Ozone, Filtration using Biologically Active Carbon (BAC) which produces biologically stable water, Disinfection with Chlorine, pH adjustment to produce chemically stable water, the conversion of free chlorine to Monochloramine to provide a stable distribution system disinfectant and preventing water quality deterioration in the distribution system by keeping water age to a minimum.

The approach recognizes that while each individual barrier may be not be able to completely remove or prevent contamination, and therefore protect public health, together the barriers work to provide greater assurance that the water will be safe to drink over the long term.

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