The Environmental Protection Agency (EPA) on Wednesday issued the first-ever national rule to limit the presence of highly toxic "forever chemicals" in drinking water.

Why it matters: The new rule is expected to reduce drinking water exposure to the dangerous chemicals for about 100 million people and prevent thousands of related illnesses and deaths.

• The chemicals are considered especially harmful because they don't degrade in the environment.

The big picture: The new rule targets certain synthetic compounds in a class of chemicals collectively known as per- and polyfluoroalkyl substances (PFAS).

• PFAS have been linked to cancers as well as immune and developmental damage in children, among other harms, per an EPA press release.
• The rule imposes the first national, legally enforceable limits on PFAS in drinking water and requires public water systems to monitor their levels.
• Public water systems have five years to implement solutions to reduce PFAS in their water.
• Starting in 2029, water systems with levels of PFAS that violate the regulation will be required to notify the public and take action to reduce the levels of PFAS.

Zoom in: EPA announced Wednesday it is also making $1 billion in funding available via the Bipartisan Infrastructure Law to help states and territories implement PFAS testing and treatment.

Zoom out: At least 45% of U.S. tap water is estimated to be contaminated with PFAS chemicals, according to U.S. Geological Survey research published last summer.

• PFAS contamination exposure in drinking water has also been found to disproportionally affect Hispanic and Black communities.
• PFAS have also been used extensively in nonstick, water- and oil-repellent and fire-resistant consumer products.