California’s water quality issues are most severe in the San Joaquin Valley and Central Coast Regions, and smaller water systems face more challenges than larger suppliers, according to a new first-ever statewide analysis of drinking water.

California has the fifth largest economy in the world, but more than 1 million of the state’s nearly 40 million people don’t have access to safe and affordable drinking water.

The California Office of Health Hazard Assessment looked at 2,903 community water systems across the state that serve at least 15 year-round connections and evaluated them based on contaminant exposure levels, sustainability, and cost...