Water Quality
"People get used to what they are drinking, and don't know the difference." - Local Official
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When the Numbers Don't Add Up
As research into Dedham's drinking water has continued, questions have emerged about how some information in the Water Quality Report provided by the Dedham-Westwood Water District (DWWD) is presented, and the difficulty residents have with interpreting presented data correctly. One clear example involves nitrate levels in the 2024 Water Quality Report.
If you review the nitrate table in the 2024 report below, several important points need clarification (click on graphic to expand):
WaterQualityNitrateTable.pngNitrate testing is conducted once per year, typically during the January–March timeframe.
The reported values combine results from two different treatment plants, each supplying different volumes of water to the community.
The “average” shown in the table does not account for those differing water volumes. In effect, the calculation treats both sources equally, regardless of how much water each contributes. (An analogy would be mixing 1 gallon of alcohol with ½ gallon of water and reporting the result as 50% alcohol – without accounting for volume.)
Nitrate levels are seasonal, often influenced by fertilizer use and stormwater runoff, and are typically lowest during winter months, when testing currently occurs.
When DWWD was asked whether the Water Quality Report could be adjusted to reflect volume-weighted averages – and whether nitrate testing could be scheduled to better align with warmer-weather fertilizer use – it was explained that the current reporting and testing meet EPA and Massachusetts DEP requirements, and that no changes are planned.
This issue warrants further review by the Select Board. The nitrate example is a straightforward case that may point to a broader concern: what is legally compliant at the federal and state level may not fully reflect local conditions or best protect resident health, particularly given Dedham’s unique two-watershed system.
Given the documented health risks associated with elevated nitrate exposure, it would be in the community’s interest for Water Quality Reports to better reflect what residents are actually consuming. More representative averaging methods, more frequent testing, and testing timed to periods of higher risk would provide clearer, more actionable information.
It is also important to recognize that water from the two treatment plants blends only partially within the distribution system. As a result, residents living closer to a given treatment plant are more likely to experience water quality closer to that plant’s measured levels than to any system-wide “average.” Providing separate water quality metrics for each treatment plant within the Water Quality Report would offer greater transparency and more meaningful information for the community.
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