Naturally Occurring Radionuclides to Determine Distribution System Water Age

Waples JT, Bordewyk JK, Knesting KM, Orlandini KA. Using naturally occurring radionuclides to determine drinking water age in a community water system. Environmental science and technology. 2015 Jul 22.

Drinking water quality in a community water system is closely linked to the age of water from initial treatment to time of delivery. However, water age is difficult to measure with conventional chemical tracers; particularly in stagnant water, where the relationship between disinfectant decay, microbial growth, and water age is poorly understood. Using radionuclides that were naturally present in source water, we found that measured activity ratios of 90Y/90Sr and 234Th/238U in discrete drinking water samples of known age accurately estimated water age up to 9 days old (σest: ± 3.8 hours, P < 0.0001, r2 = 0.998, n =11) and 25 days old (σest: ± 13.3 hours, P < 0.0001, r2 = 0.996, n =12), respectively. Moreover, 90Y-derived water ages in a community water system (6.8 × 104 m3 d-1 capacity) were generally consistent with water ages derived from an extended period simulation model. Radionuclides differ from conventional chemical tracers in that they are ubiquitous in distribution mains and connected premise plumbing. The ability to measure both water age and an analyte (e.g., chemical or microbe) in any water sample at any time allows for new insight into factors that control drinking water quality.

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