Warmer temperatures, stagnant supply prompt Hamilton to add more chlorine to drinking water

Warmer temperatures and stagnant liquid in the city’s distribution system have prompted Hamilton to up chlorine levels in its drinking water.

Director of water Nick Winters revealed the slight increase in the disinfectant is to tackle “chlorine degradation” – when the element dissipates through non-activity, increasing temperatures or a combination of both.

“When folks aren’t watering their lawns and using potable water … we have seen challenges over the past few years with chlorine degrading in some of the outer reaches of our system,” Winters explained.

He says the city resorted to flushing out much of the system in 2021, like the fire hydrant infrastructure, to replenish “old water” stuck in some areas for around three days at a time.

Regular monitoring that year saw a higher number of adverse water quality incidents tied to low chlorine.

“So if we don’t use enough water across the city, then the water sits there. The longer it sits there, chlorine degrades,” Winters said.

“There’s (also) impacts from water temperatures and that’s something that we’ve seen over the past few years, is that the temperatures of Lake Ontario are increasing earlier in the year and staying warm longer.”

Hamilton didn’t see the same issues in 2022 due to lower-than-normal precipitation and colder temperatures.

The city applied for and received approval in 2023 from the Ministry of the Environment (MECP) to increase levels of chlorine at the Woodward Water Treatment Plant as a backup to avoid similar issues experienced in 2021.

Winters says they’ll be bumping chlorine levels this summer to 2.9 milligrams per litre from the previous 2.7, and possibly going from 2.5 milligrams per litre to 2.7 in the winter months.

“We aren’t adding more chlorine to the city’s water than the typical ministry threshold of three milligrams per litre,” Winters said.

“It’s an extra tool in our toolbox for how we manage the challenges in our system with water age and water temperature.”

The federal and provincial governments jointly share responsibility for providing safe drinking water and Health Canada has sanctioned the use of chlorine supplies for over a century.

“Disinfecting our drinking water ensures it is free of the microorganisms that can cause serious and life-threatening diseases, such as cholera and typhoid fever,” the agency’s website says.

However, it does connect chlorine with trihalomethanes (THMs), a group of chemicals that can contaminate drinking water typically when water comes in contact with natural matter, like decaying leaves.

THMs have been linked to some cancers and reproductive problems in humans but are generally considered low-risk.

Ozone and UV treatments are other methods municipalities can and have used along with chlorine to inhibit the growth of harmful microorganisms while improving taste and other qualities.

Winters believes it’s unlikely Hamiltonians will “notice any significant change” in the community’s supply.

“Despite the additional chlorine … we do have granular activated carbon at our water treatment plant, which does a great job removing taste and odour components that generally come from algae components,” he said.