Is climate change a risk to Hamilton’s drinking water?

The city blames record Lake Ontario temperatures this fall for repeated drinking water tests that showed chlorine levels below provincial safety standards - a problem climate change threatens to make worse.

Hamilton recorded seven adverse water quality incidents" in October and early November - mostly from tests in Dundas, Ancaster and on the Mountain - that showed chlorine levels below provincially mandated standards.

The city must report those incidents to the province and public health, but so long as full chlorination is quickly restored, public notification is not required. There were more reportable incidents in a single month this fall than in any full year between 2015 and 2019.

The city believes it has diagnosed the problem: a Great Lake water source that is running a fever.

What we've seen is that as (lake) temperatures stay warmer later into the season, it's harder to maintain our target chlorine residuals," said acting city water director Nick Winters, who added the problem was also noticeable last year. We expect that it could become a trend."

In mid-October, average Lake Ontario surface temperatures hovered at 18.5 degrees C - the warmest at that time of year since the 1990s, according to records at the U.S. National Oceanic and Atmospheric Administration.

The unusual number of low-chlorine results has spurred a study to see if the city needs to change how or where drinking water is treated - especially since global warming is expected to heat up the Great Lakes over time.

Lake Ontario broke heat records last summer and average temperatures have inched upwards for years - a trend climate change models suggest will continue, said Gail Krantzberg, a McMaster University environmental engineering professor and Great Lakes expert.

That could create a whole slew of consequences" for lake communities in future, she said, including declining fish populations, unsafe beaches, wilder weather and yes, water treatment woes.

Maintaining the right level of chlorination is one challenge, Krantzberg said - but municipal water treatment also faces the growing threat of algae and cyanobacteria that thrive in warmer waters. The former creates a musty" taste and odour, but the latter can produce dangerous toxins.

The city sources drinking water from Lake Ontario and treats it with chemicals like chlorine before pumping it out to reservoirs and water towers across the old city and suburban Hamilton.

Chlorine decays faster in warm water. That rarely matters in the summer, because hot-weather activities like lawn watering and pool-filling ensures drinking water doesn't sit around for long.

But resident don't use as much water in the fall - especially the rainy autumn we had in 2021. Winters said the spike in adverse incidents is likely due to chlorine decaying faster in warm water that was stored for longer periods.

We're able to manage that," he said, stressing city staff sample daily throughout the sprawling distribution system to ensure the water that reaches your tap is safe. But for now, managing the problem means wasting a lot of treated water.

Specifically, when the city records a low-chlorine test result, it is required to flush the system like crazy" with fresh treated water - and also dump into the sewers stored water that has aged out prematurely.

That regular flushing accounts for some of the 26-percent of treated water - billions of litres - that is lost" in Hamilton's distribution system before it ever gets to your tap.

Winters said next year's study will ideally provide recommendations on future treatment protocols. What it might mean is in future we need to disinfect at more locations," he said.

What is an adverse water quality incident?

An AWQI occurs whenever treated water fails to meet provincial safe drinking water standards. Every AWQI spurs a requirement to notify the province and local public health unit - but not necessarily the public.

For example, if a drinking water system test detects E. coli bacteria - which can cause illness or even death if ingested - the city must warn the public to either boil water or use alternatives until the problem is solved.

For low-chlorine test results, the city must flush the distribution system - but if that does the trick, no public alert is needed.

Matthew Van Dongen is a Hamilton-based reporter covering transportation for The Spectator. Reach him via email: mvandongen@thespec.com