This study examined the association between public water system PFAS detections and serum concentrations among a general population of Southern California adults. We found that PFAS detections in public water systems were associated with higher serum PFAS concentrations. Our findings suggest PFAS contamination in drinking water may be a significant contributor to serum PFAS levels, even among communities without high level contamination from industrial manufacturing. These results support drinking water monitoring initiatives in California to understand PFAS contamination and mitigate exposure.