Water Quality Test Results
On November 30, 2019, after consultation with the State’s Division of Drinking Water, the City of Poway issued a precautionary boil-water advisory for its drinking water in response to reports of “cloudy” or “discolored” tap water by some customers. Different factors could cause discolored drinking water including corrosion of iron pipes in the distribution system or indoor plumbing but could also be caused by the intrusion of untreated water into the drinking water system. The latter is clearly of greater concern because the untreated water could contain harmful bacteria or other microorganisms that are of public health concern. The precautionary boil-water advisory was issued out of an abundance of caution in case the discolored water was caused by the intrusion of untreated water into the system.
Over the following 7 days, the City collected 255 samples of water from a number of residences, businesses, and our distribution system storage facilities and analyzed them for two primary types of water quality parameters: the first was the disinfectant level to ensure that the water continued to be properly disinfected, and the second was for the presence of bacteria in the water. The significance of these two tests is presented below, along with all the official laboratory reports containing the results. The locations from which the samples were taken have been redacted to respect the privacy of residents and to maintain the security of the water system. Needless to say, all the samples were collected from the City’s drinking water system.
All samples were analyzed by ALS Truesdail Laboratories, Inc., which is a State-Certified laboratory located in Irvine. The City contracts with Truesdail laboratories for water analysis that is performed on a regular basis. The first two pages of each report is a summary list of the samples presented in that report, and the results begin on the third page. The results of each sample are presented separately in the report, and the following header is shown above the results reported for each sample:
The following is the meaning of each label in this header:
Analyte – refers to the parameter measured, including chlorine, bacteria, and others.
Result – is the measured value of each parameter.
RL – refers to the “reporting limit.” This is the minimum level that the laboratory can measure with confidence.
Units – refers to the measurement units of the reported result. For example, for chlorine, the unit is “mg/L,” which is milligrams of chlorine per liter of water. This is the same unit measurement as “ppm” or “parts-per-million” that some use.
The remaining labels (DF, Batch, Analyzed, Analyst, Method, and Notes) are technical specifications that the laboratory uses to identify how each sample was analyzed, who analyzed it, and when.
Below each header, the analyses conducted on each water sample are divided into two sections: “Field Measurements” and “Microbiology” as shown in the example below:
The following are explanations of each parameter analyzed to help you understand what the results mean:
“Chlorine, Total” – The drinking water disinfectant used by the City is “chloramine,” also referred to as “chlorine.” This is the same disinfectant that is used by almost all water systems in the counties of San Diego, Orange, Los Angeles, and many others across the State. All drinking water systems in the United States are required to maintain a measurable disinfectant level in the water distribution system. Chlorine levels in the City’s drinking water may range from less than 0.1 mg/L to as high as 4.0 mg/L. Chlorine levels higher than 4.0 mg/L may be present in some samples, but the Federal and State regulations mandate that the average chlorine level across the entire water system should not exceed 4.0 mg/L. In the example shown above, the chlorine level was measured at 3.10 mg/L (listed under “Result”).
“Total Coliforms” – This is a type of microbiological analysis that all water systems are required to conduct on their water. This analysis detects a type of bacteria whose presence indicate the potential prevalence of unsanitary conditions in the water system. The analysis conducted reports the bacteria as either “Present” or “Absent.” In the sample reported in the example above, the “Total Coliforms” are reported as “Absent.” Coliform bacteria were absent from all of the 255 samples collected during this incident, except one location designated as “R14.” The sample collected on 12/3 suggested the presence of coliform bacteria. Follow-up confirmation samples were collected on 12/4, 12/5, and 12/6, all of which contained no coliform bacteria.
“Plate Count” – This is another type of microbiological analysis that looks for the presence of natural bacteria in the water. The bacteria detected by this analysis are not necessarily harmful to humans or animals, but their levels are preferably maintained low or non-detectable. In the example shown above, the “Plate Count” result is shown as “ND,” which stands for “not detected.” Of the 255 samples analyzed between November 30 and December 6, only three samples contained detectable levels of these natural bacteria, which is not uncommon in water distribution systems.
“E. Coli” – This is the type of bacteria that is of the greatest concern and is the same type that one hears about in news reports of contaminated foods. The analysis conducted by the laboratory reports the “E. Coli” bacterial level as either “Absent” or “Present.” In the example above, the result for “E. Coli” is listed as “Absent” under the “Result” heading. E. Coli bacteria were absent from ALL the samples collected by the City between November 30 and December 6.
Finally, it is important to emphasize that the public health risk caused by the intrusion of untreated water into a water distribution system is a serious matter. This incident is a solemn reminder to us of the huge responsibility drinking water providers have and the critical role we play in protecting public health. We will continue to work with the State’s Division of Drinking Water to identify and remove any potential vulnerabilities from the City’s drinking water system.