A Boulder ballot measure that would change the city’s water quality standards appeared headed for defeat Tuesday night.

As of midnight, Boulder ballot measure 2B had garnered 8,044 votes, or 42 percent, in its favor, and 10,902, or 58 percent, against it. But with fewer than half of Boulder County’s votes tallied, supporters said they weren’t ready to give up.

Randall Weiner, the man behind 2B, said he was confident the potentially thousands of votes that hadn’t yet been counted would bring his measure to victory. And even if uncounted ballots don’t tip in 2B’s favor, Weiner said the campaign still will have succeeded in raising public awareness.

“We’ve succeeded in getting the powers-that-be and the voters to recognize that contaminants are an important issue,” he said.

The question would require that any substance the city adds to the water meet “maximum contaminant level goals” set by the federal government for certain toxins. It would end the city’s current practice of using hydrofluosilcic acid to fluoridate the water supply, because the substance contains arsenic and lead in quantities well below what the government allows for the purposes of regulation, but still above the federal goal of zero.

It also would require any substance added to the water to be approved by the U.S. Food and Drug Administration.

The latter requirement was the source of disagreement between supporters and opponents of the measure. Supporters said the city could use substances the FDA had approved for human use, but opponents said the provision was a poison pill that would make it impossible to fluoridate the water, because the federal agency doesn’t regulate water additives.

Opponents said the measure’s real aim was removing fluoride, not cleaning up the water supply.

Linda Wilkinson, who headed up the “No on 2B” committee, said Tuesday night’s numbers showed voters understood the measure’s real impact and rejected it.

“I think we just have to thank Boulder voters for being perceptive and educated on the subject,” she said. “They looked at the issues and saw the deceptiveness of the initiative.”