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The Trump administration reached for a strange metaphor about spiking the punch while arguing to limit the Clean Water Act before the Supreme Court. Also the murder-mystery writer Agatha Christie came up.

The case in question, County of Maui v. Hawai’i Wildlife Fund, involves a wastewater treatment facility in Maui that’s sending sewage runoff into the Pacific Ocean. That sewage is destroying coral reefs off the island’s west coast, but the county is arguing — with the help of the Trump administration — that the sewage isn’t subject to regulation under the Clean Water Act because it runs through local groundwater before hitting the federally regulated ocean waters.

To explain what’s going on, Malcolm Stewart, a lawyer for the Department of Justice, told the justices to imagine how they might discreetly spike the punch at a party with whiskey.

“If, at my home, I pour whiskey from a bottle into a flask and then I bring the flask to a party at a different location and I pour whiskey into the punch bowl there, nobody would say that I had added whiskey to the punch from the bottle,” Steward said before the Supreme Court Wednesday.

Lawyers on the other side of the case essentially said: Thank you for making our point for us.

Following along with the metaphor, David Henkin, a lawyer for the environmental group Earthjustice, noted that with the Clean Water Act, Congress was attempting to keep whiskey out of the punch entirely — whiskey being pollution, and the punch, federally regulated waters.

“So if all of a sudden you tasted the punch and you said, ‘This tastes like whiskey.’ You'd say, ‘Where did that come from?’” Henkin said. “You'd say it came from the whiskey bottle. That's how we know it's whiskey.”

Henkin’s team is arguing that allowing unregulated pollution to first flow through groundwater before entering waters covered by the Clean Water Act would open a huge loophole for polluters. All they’d have to do is cut their pipes short and send their runoff through groundwater. But the Trump administration and the County of Maui worry that if pollution that runs through groundwater is regulated a whole other set of sites might need permits.

At the hearing, the justices also discussed how, if you can’t identify a single source of pollution, it falls under a different set of rules. Take, for example, a neighborhood in which everyone has a septic tank and they’re all leaking, no single person or business can necessarily be held solely responsible. That prompted a murder-mystery metaphor.

“It's an Agatha Christie novel,” Chief Justice John Roberts said. “You have 20 people and they all shoot the gun at the guy at the same time.”