Environ. Sci. Technol. 2008, 42, 8171
Response to Comment on “Nitrification in Premise Plumbing: Role of Phosphate, pH, and Pipe Corrosion”. Study Used Conditions That Are Realistic and Representative We disagree with Mr. Brown’s statement that the experiments were a “set up” not representative of actual conditions present in some consumers’ homes. First, while it is true that most utilities dose chloramine and chlorine disinfectant to water at the treatment plant, the chlorine residual disinfectant can disappear completely by the time the water reaches many home plumbing systems. This is one reason that the National Research Council recently identified problems in premise plumbing as a high priority for future research (see Chapter 8, of the National Research Council Report (NCR) Drinking Water Distribution System: Assessing and Reducing Risks). That report also contains data illustrating that, even if free chlorine or chloramine are present in the water coming into the homes, it can disappear very rapidly via reactions with home plumbing systems as it sits in the pipe. Hence, our testing without any disinfectant present is perfectly representative of what occurs in many homes. The longer stagnation or storage times used in our tests occur routinely in plumbing when consumers do not use their water overnight or during vacations. Second, this research was funded by the United States Environmental Protection Agency and the Awwa Research Foundation (AwwaRF), in large part, because of widely recognized “real world” problems with nitrification. Rampant nitirification occurs in many water distribution systems that use even very high levels of chloramine (>3 mg/L). Even without stagnation and in the presence of this high chloramine, nitrifiers become established in water mains and
10.1021/es802010p CCC: $40.75
Published on Web 09/24/2008
2008 American Chemical Society
distribution systems and there are dozens of peer reviewed papers on this subject (see for example, the EPA white paper currently at http://www.epa.gov/ogwdw/disinfection/tcr/ pdfs/whitepaper_tcr_nitrification.pdf). Third, there are several case studies in the literature that document large pH drops occurring overnight in premise plumbing due to nitrification and other reactions. For example, we have recently published data collected from “real” consumer homes, in which the pH dropped more than was reported in our paper (see Zhang et al., ASCE Journal of Environmental Engineering, July 2008, page 521). Specifically, we recorded a drop in pH in some homes in Maui, Hawaii from 7.89 to 6.77. In Washington DC.the pH dropped from 7.9 to 6.7 in some instances. We have even seen cases where the pH in home plumbing dropped to 5.2, although we do not yet fully understand the circumstances which contribute to these very large pH decreases. These large pH drops in home plumbing have been observed in situations where up to 4 mg/L free chloramine disinfectant residual (the highest level allowed by law) was present in the water that is supplied to the building. In conclusion, our study is perfectly consistent with, and can explain, many practical published observations regarding the prevalence and occurrence of nitrification. The results are also consistent with several real world observations regarding lead and copper corrosion issues that occur in systems plumbed with and without plastic (as per the Kimbrough study). The notion that our results are “speculative” and have little to do with real-life is simply incorrect.
Marc A. Edwards Virginia Polytechnic Institute and State University, Department of Civil and Environmental Engineering, Blacksburg, VA, 24061-0246 ES802010P
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