How much of a problem are off-tastes and odors in Napa’s city tap water? And how easy or difficult are they to measure?
Responding to a Napa County Grand Jury’s call for improved water treatment, a city report last week defended its handling of quality issues that do not pose health risks but instead make water less pleasing to the palate and nose. The statement of reply – which cities must issue within 90 days of a grand jury report – outlined the measures Napa takes to control the sources of taste and odor problems, particularly algae that are commonly found in reservoir supplies before treatment.
Issued in June, the grand jury report “Napa County Water Quality: It’s a Matter of Taste” found that drinking water in Napa and other local cities meets state and federal safety standards, but found issue with taste and odor, including from algae amounts of as little as 10 parts per trillion in treated water.
Napa manages algae levels with a combination of aeration, increasing the amount of pre-oxidant and switching to state-supplied water from the Sierra Nevada, according to grand jury response letter signed by City Manager Steve Potter. However, Napa officials also pointed to the speed with which algae levels can wax and wane faster than water samples can be analyzed.
“Species, growth and lysis of algal cells can change in a matter of minutes and without warning,” the city reply states, pointing to the 10 to 14 days laboratories need to analyze odor-causing compounds in water samples. “… Analyses can and are currently used as guides, along with color and algal speciation, but not all (taste and odor) occurrences are predictable. By the time results are received, the water quality may have already changed multiple times.”
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Separate treatment systems serve each of Napa’s three water sources – the main municipal reservoir at Lake Hennessey east of Rutherford, the smaller Milliken Reservoir, and the city’s allotment from the State Water Project drawn from Sierra Nevada snowmelt.
The city report announced Napa is in the planning stage of a treatment-plant upgrade at Lake Hennessey, expected to start in 2022 that will cost at least $10 million and will, in part, address odor and taste issues. A joint city-county study of reservoir watersheds and winter runoff is planned to begin this fall.
Napa officials also disputed the grand jury’s characterization of off-colors in city water, saying such problems show up only during its annual pipe flushing program or after water main breaks.
The city’s letter also addressed communication with water customers, which jurors described as erratic and sometimes lacking at all of Napa County’s five municipalities. Grand jury recommendations included a formal written policy on handling water quality inquiries, including issuing a written notice for every complaint filed.
Because complaints about tap water can be subjective and often result from problems inside a building rather than with city pipes or equipment – in-home water heater, filter or softener malfunctions, for example – city staff time often is better spent resolving customer questions in person or by telephone, officials said.
“The city does not intend to provide a written response for every complaint, since that would not result in an efficient use of ratepayer funds,” the city said in its response letter.