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Tier 1 violations of national primary drinking-water regulations. The graph in A shows the number of Tier 1 violations for each week during the 2006–2015 study period. Violation counts are presented separately for those attributable to 2 categorizations—nitrate (dashed gray line) and pathogens (solid orange line). The map in B depicts county-level, Tier 1 violations water sales per CWS, during the 2006–2015 study period.
