More water testing confirms high levels of lead at Yellowknife's William McDonald school

High levels of lead have been confirmed in the water at William McDonald School in Yellowknife after another round of testing.

The N.W.T.'s chief public health officer has formally issued do-not-consume orders for the water at William McDonald, as well as Range Lake North. The orders come a month after parents and staff at the schools were informed high lead levels had been detected at both schools.

On Wednesday, the school board sent another update to parents saying additional testing was completed on May 27 as well as June 12 and 13. Yellowknife Education District No. 1 (YK1) said a "flushing protocol" to let the water run briefly before use would be required at Range Lake North.

It said more work will have to be done to identify where high lead levels are coming from at William McDonald, and identify how to mitigate it.

"The water system will remain closed for drinking until these steps are completed," YK1 wrote.

Shortly thereafter, the N.W.T. government released the results of its follow-up testing in a news release.

The government said it had two types of tests done: random sampling, "to get a snapshot of lead levels during normal water use," and something called exceedance protocol testing — basically, a "stress test" that's more likely to show higher levels of lead.

Both tests showed elevated lead levels at parts of William McDonald. Only the stress test showed high results at parts of Range Lake North.

What do those tests mean?

At William McDonald, random sampling showed seven of 13 spots had elevated lead levels. Some were up to four times higher than Health Canada's recommendation of no more than five micrograms of lead per litre.

The highest level was found in a staff room sink on the second floor, where lead levels measured 20 micrograms per litre.

The stress test, however, showed significantly higher results. That test was measured in two ways: water that had sat overnight for eight hours, to replicate how lead could leach into the water from plumbing; and water that was collected after the tap was flushed for five minutes, followed by half an hour of sitting, which was meant to replicate regular conditions.

A sink in a media room on the school's first floor showed 566 micrograms per litre in water that had sat — more than 100 times Health Canada's recommended amount — and 105.7 micrograms after the tap had been flushed.

Two locations on the second floor showed higher lead results after being flushed than after sitting.

Range Lake North, on the other hand, only showed elevated lead levels during the stress test, and only in water that had sat overnight. Three of 12 testing spots showed lead levels between 5.8 and nine micrograms per litre.

Ongoing assessment

The territorial government said the results are part of an ongoing assessment of lead in school drinking water systems being conducted by engineering and environmental consulting firm Stantec. It said the final report summarizing the findings is expected "shortly."

The release says that "most children who have lead in their blood do not show immediate symptoms." 

"However, even low levels of lead can result in subtle neurodevelopmental issues, particularly in young children."

The update also cited recent health monitoring by the University of Ottawa and University of Waterloo that tested residents in Yellowknife, Ndılǫ, and Dettah from 2017 to 2024. 

It found lead levels in children and parents to be low. 

The release said the territorial government will continue to share updates on the situation. 

"We understand that many families, educators, and community members will have questions," the release said.

"While the final Stantec report is still pending, this update reflects test results that support the continuation of existing mitigation measures. We will continue to keep residents informed and will share verified updates — including the final report — as soon as they are available."