“Nitrate-contaminated groundwater is now pervasive in agricultural areas in California such as the San Joaquin and Salinas valleys. It’s a serious problem in rural communities that rely solely on wells for drinking water…most nitrate pollution comes from crop runoff – 55 percent from synthetic fertilizer [industrial agriculture] and 33 percent from animal manure [industrial dairy] – according to a University of California, Davis study commissioned by the State Water Resources Control Board.”
Holistic, regenerative agriculture helps mitigate this problem.
https://www.newsdeeply.com/water/articles/2017/08/31/why-californias-nitrate-problem-will-take-decades-to-fix