South Slave water advisory believed related to organics getting into the system

A drinking water advisory issued in parts of the N.W.T.’s South Slave this week may be related to low water levels in the region, officials say.

Glenn Smith, senior administrative officer with the Town of Hay River, said the town’s water treatment plant could be taking in more organics like leaves, algae and soil, because of the low water.

Officials believe chlorine reacting with those organics are responsible for elevated levels of disinfection byproducts called trihalomethanes (THMs), which prompted the water advisory.

On Monday, the N.W.T.’s chief public health officer issued the advisory warning residents in Hay River, Enterprise, Kátł’odeeche First Nation and Kakisa of THMs in the water. 

THMs can form when chlorine, which is used to disinfect water, reacts with naturally occurring materials. 

Residents of those South Slave communities have been advised to either:

• use a pour-over filtration water pitcher like a Brita;
• fill a pitcher with water and leave it in the fridge for 24 hours without covering it before consuming it — allowing the trihalomethanes to partially evaporate;
• install filters on their taps that are certified to remove trihalomethanes — labeled with a NSF/ANSI 53 certification;
• or use carbon filters that are mounted on the tap or under the sink.

Exposure to THMs can affect human health over the long term. The N.W.T.’s chief environmental health officer, Chirag Rohit, said exposure can increase the risk of cancer, but that’s after 70 years’ worth of exposure to high levels of THMs. 

The risk associated with short-term exposure, he said, is “very low.”

Working to resolve the issue

The water samples that prompted Monday’s advisory show THM levels just slightly above the national standard, according to Smith. 

He said engineers and specialists with environmental health and with the territory’s Department of Municipal and Community Affairs are in Hay River this week working to resolve the problem. 

They’re looking at adjusting chlorine doses and air exposure, which affects THM levels — similar to the advisory’s recommendation of leaving an uncovered water pitcher in the fridge. 

Smith said the issue is not related to the town’s water treatment plant, but resolving the THM levels is made more difficult by the plant’s age. He said the plant is 40 or 50 years old and uses older technologies. 

“It can be a bit challenging in some cases to treat and balance the changing conditions,” he said.       

Rohit, the environmental health officer, said the territory issued the advisory so residents could be aware of what’s happening with their drinking water and make informed decisions to reduce exposure, but said residents don’t seem to have been exposed for long. 

“Slave Lake over the years, the water that we are taking in for the treatment plant, that’s changing. It’s beyond anyone’s control,” he said. 

He said it’s difficult to predict when the advisory will be removed. He said the town plans to take samples in the next week or two but that it takes time to have those samples tested.

In the meantime, Rohit said there is also a risk with inhalation of THMs and recommends running a fan while showering or bathing. He said the water is still safe to use for brushing teeth, washing hands, laundry and other household tasks. 

The Town of Hay River is holding a public meeting Thursday at 7 p.m. in the community hall to answer residents’ questions.