The City of Whitehorse is facing a pricey upgrade to its water treatment system, after officials noticed changes in the quality of the city's groundwater in recent years.

The proposal is to add a new filtration system, at a price of about $39 million — and the city is not yet sure where that money will come from. There's also a timeline, as the work would need to be done before the city's water licence comes up for renewal in five years.

"At no time is our water not safe to drink," said Mike Firlotte, the city's water and wastewater services manager.

"We just want to make sure we're proactive going into the future and if regulations change or the water quality gets worse, that we're ready for it."

Right now, all of the city's drinking water comes from the Selkirk aquifer in Riverdale, and its seven groundwater production wells. The water is chlorinated before distribution.

City officials say that system has served the city well, but recent years have shown evidence that surface water — from the Yukon River — is sometimes getting into the groundwater source.

"We've seen ... different fingerprints of water coming through our wells," Firlotte said.

That's an issue because territorial regulations for treating drinking water differ depending on the source of that water. If surface water is getting into a groundwater source, even in small amounts, then the water requires treatment as though it's all surface water. Right now, Whitehorse is only equipped to treat and distribute pure groundwater.

If the city did nothing, it's conceivable that in the future some of its production wells could be taken out of service for periods when there's evidence the water is not safe. That could have a serious impact on the overall supply of potable water in the city, with potential boil-water advisories.

"We'd still be able to deliver water, but there could be a risk at the water might not be potable as we need it to be — and that's the risk," Firlotte told a standing committee of city council this week.

"When you have surface water mixed in with your groundwater, it's not as pure. There's contaminants, in regards to biological issues ... our current treatment process will not protect our customer."

The new system will also offer redundancy to the city's water supply, Firlotte said. Once the city is equipped to treat surface water as well as groundwater, it could draw water from Schwatka Lake as needed — instead of relying solely on groundwater from the Selkirk aquifer.

City staff had earlier proposed a $60-million fix, but council asked them to see if there was a cheaper option. That's when staff came up with the new, $39-million option presented to councillors this week. According to Firlotte, it would add a new filtration system to the existing infrastructure, allowing the city to adequately treat surface water as well as groundwater.

Mayor Laura Cabott praised city staff for finding a slightly cheaper option.

"There's no question that is very, very expensive, but I do think that's quite commendable," she said at Monday's committee meeting.

"We need to keep moving. Water has got to be the number-one priority for, or maybe one of the top three, for [a] municipality."

Still, it's not clear where the money will come from, and work likely can't begin until the funding is secure.

City staff told council that the city's current water licence is up for renewal in 2028, and a new system would likely need to be in place by then. That means work should ideally begin by 2026, they said.