California wants to slash the allowable levels in drinking water for two “forever chemical” compounds, immediately prompting agencies supplying water to 2.5 million residents in Orange County to remove a fifth of their wells from service.

The State Water Resources Control board Thursday said it planned to dramatically lower its response levels for perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), though actual drinking water standards are still years away.

The response levels require water suppliers to install treatment, and remove wells from service if they exceed the thresholds. Notifying customers is required if districts plan to keep wells in service without treatment for an extended period.

Orange County oversees the area’s groundwater basin and provides water to 19 agencies, which rely on underground supplies for 77% of deliveries. The remainder comes from the Colorado River and Metropolitan Water District of Southern California, which supplies water to 19 million people in the region.