The authors identified constituents from 18,506 public groundwater wells in all 58 California counties measured in 1996–2010 . They obtained county-level kidney cancer incidence data from the California Cancer Registry for 2003–2017 . 13 groundwater constituents met stringent WWAS criteria (a false discovery rate of 0.10 in the first cohort, followed by p values <.05 in subsequent cohorts) The standardized incidence ratio furthest from a null was for bromide (0.97)