A new study has found drinking water in California’s agricultural core is contaminated by nitrates and that the problem is likely to worsen in the coming years. Researchers at the University of California, Davis, found chemical fertilizers and livestock manure are the main sources of groundwater contamination affecting more than one million people across the state’s Salinas Valley and parts of the Central Valley. Nitrates are linked to a range of health problems, including reproductive disorders and cancer, and high levels of nitrates in water can prove deadly to infants.