AMNA NAWAZ: For the first time, the federal government is on the cusp of regulating a class of deadly so-called forever chemicals out of America's drinking water.

The EPA's proposal applies to six of those chemicals known as PFAS compounds, and would require water utilities to clean any detectable level out of their systems.

Doing so could cost billions, and thousands of their chemical cousins would remain unregulated.

Annie Snider covers this closely for Politico, and she joins me now.

Annie, welcome, and thanks for joining us.

Let's back it up here a little bit, though.

There are thousands of these PFAS chemicals.

Drinking water is just one place that they're found.

So where else do we find them?

How common are they?

ANNIE SNIDER, Politico: They are extremely common.

They have been in widespread consumer use since the 1940s.

They have an extremely strong chemical bond that makes them very useful for commercial purposes.

They have been used in nonstick cookware.

You know you're not supposed to use your knife in a Teflon pan.

That's because of these chemicals.

They have been used in camping gear, stain-resistant carpeting, military firefighting foam that's been sprayed at bases and installations around the country and at airports around the country.

They are ubiquitous in the environment.

And because of that very strong bond that makes me so useful, they're also extremely difficult to break down in the environment.

So once they're there, they typically stay there and they bioaccumulate.

That's not just in the environment in the rivers and streams where we get our water.

It's also in American blood.

We breathe them in.

We eat them in our food, and they're in food packaging as well.

And we also get them through our drinking water.

AMNA NAWAZ: So why would we want to regulate them out?

What do we know about the links between some of these chemicals and negative health impacts?

ANNIE SNIDER: Yes.

Well, as you mentioned, there are thousands.

There's estimated to be 12,000 chemicals in this class.

Many of them, we know virtually nothing about.

But we do know something about some of them.

The best studied chemicals, these two that have been in production since the -- that were in production since the 1940s, have been pretty clearly linked with cancer and other health ailments, things like high blood pressure, developmental impacts, problem birth defects, and also immune system effects.

One of the kind of more interesting effects that we see at extremely low levels of exposure is an impact on the immune system that makes vaccines less effective.

AMNA NAWAZ: So, the EPA is saying they're going to be regulated up to detectable levels, does that mean lower levels are considered safe?

ANNIE SNIDER: Not exactly.

So, EPA's proposed regulation here would limit six PFAS.

Two of these chemicals, the two that I mentioned earlier that are the most well-understood and are actually no longer in production, would be limited to detectable levels.

So EPA has actually said that levels even 1,000 times lower than what can be detected are still dangerous to human health, can still cause negative health impacts.

But, practically speaking, all that they can require is for utilities to monitor for these chemicals and, if they find them, treat them so thoroughly that they're below those detectable limits.

The other thing that EPA did in this regulation is include limits for four other types of PFAS chemicals.

And some of these are chemicals that are still in commercial use.

In fact, two of them are the ones that the chemicals industry turned to when they phased out those two older chemicals.

And for those, EPA is taking sort of an innovative approach, which acknowledges that these chemicals might have more severe health effects in combination than they do individually.

AMNA NAWAZ: So, Annie, we know some states have already moved to regulate these compounds to some degree, but this is a proposed federal standard.

How easy would it be for water utilities to meet these new standards?

What would it take?

ANNIE SNIDER: Technologically speaking, there are absolutely technologies that drinking water utilities could install that would treat for these chemicals that are pretty well-proven.

We have got things like granular activated carbon and reverse osmosis.

The technologies are there.

What they are not is cheap.

They are very expensive to install in the first place.

And they also have ongoing operational costs.

And the way that our law is set up right now, those costs would be borne by customers.

Those would show up on people's regular monthly or quarterly water bills.

They would not be paid for by the polluters who put those chemicals there in the first place.

AMNA NAWAZ: Annie, when you step back here, how big a deal is it that there could be a federal regulation for this, knowing what we know about the potential impacts and this compound -- on the chemical compounds more widely?

How big a deal is this?

ANNIE SNIDER: It's an extremely significant step.

A little bit of context here.

The U.S. has not regulated a new contaminant in drinking water in nearly 30 years.

The Congress overhauled the Safe Drinking Water Act in 1996, and made it significantly more difficult for EPA to regulate chemicals, to regulate contaminants in drinking water.

And so, if this rule is finalized -- and that is a big if -- it would be the first major upgrade to the safety of the nation's drinking water in nearly 30 years.

And what's worth noting is, those same technologies that can treat for these PFAS chemicals would also in many cases remove other contaminants from the drinking water as well.

And so it could have some very significant improvements to the nation's drinking water overall.

AMNA NAWAZ: That is Annie Snider from Politico joining us tonight.

Annie, thank you so much.

ANNIE SNIDER: Thank you.