Sunday, September 24, 2023
September 24, 2023

Water quality reports mandated

A refocused effort targeting disinfection byproducts has Island Health officials and staff at Salt Spring’s largest water district working to gather information and take action to ensure safer drinking water. 

Trihalomethanes (THMs), such as chloroform and bromodichloromethane, are among the common byproducts of disinfection. They occur when organic matter already in lake water reacts with the chlorine added to disinfect it. THMs have also been linked to colorectal cancers, according to Health Canada; since most drinking water treatment plants in the country use some form of chlorine to disinfect drinking water, that agency has set guidelines for THMs: a maximum acceptable concentration of 100 micrograms per litre.  

While federal regulators note the health risks of THMs are far less than those from consuming water that has not been disinfected, they direct utilities — including the North Salt Springs Waterworks District (NSSWD) — to make every effort to keep THMs and other byproducts at the lowest levels possible, so long as they do so without compromising the effectiveness of disinfection. 

“This has been happening since the dawn of time, since we started to chlorinate the system,” said NSSWD operations manager Ryan Moray at the district’s May 25 board meeting. “It’s something that is being tracked more and more now by Island Health, [so] we’re working with them to meet all the limits that we’re required to.” 

The recent action seems to stem from reinvigorated efforts by Island Health to encourage the district to monitor THMs more closely — indeed, the requirement to complete the new Maxwell Lake Dissolved Air Flotation (DAF) treatment plant by 2025 stems from an effort to remove much of the organic matter that reacts to create THMs before it encounters the chlorine. Water from St. Mary Lake is currently treated through a DAF system prior to chlorination.  

The urgency also comes after a routine inspection of the Lake Maxwell water system earlier this year. That inspection in February found written records of operations and maintenance — including manual measurements of chlorine residuals at the chlorination plant and throughout Ganges — and reported that treated water samples were tested for bacteria, cyanobacterial blooms and disinfection byproducts regularly with “satisfactory” results. However, Island Health indicated it wanted more fulsome reporting specific to THMs. 

The last Annual Drinking Water Report was completed in 2018. According to Island Health, legislation requires that to be done annually, and told NSSWD the next one was due by June 30. Part of the collaborative plan going forward, Moray said, included enhanced flushing on the Maxwell system, as well as increased data gathering — and sharing with the public. 

NSSWD has been asked to trend the THM levels for the prior years, then provide reporting in collaboration with Island Health every year until the new water treatment plant is completed in 2025, said Moray, adding that the district and Island Health would collaborate on a memorandum that would be distributed to customers. 

In the last annual water quality report in 2018, the Maxwell Lake system was noted to present at a THM concentration of 135.13 ug/L, averaged across samples from multiple locations collected quarterly. That report also noted 81.3 per cent of THM samples at Maxwell were above the guideline 100 of ug/L.  

For more information on the Maxwell Lake DAF project and water quality monitoring, visit


  1. Should we be chlorinating every drop of water that goes through pipes – even if it is to flush toilets, water gardens, wash the floors etc? Less than 10% is used for drinking/cooking. Many countries around the world have drinking water delivered and do less chlorination for household water uses. A small filtration system (charcoal/UV) at source in home with a special tap that is for drinking water only is not expensive – far less than other appliances such as fridge or washing machine. Imagine the size of the chlorine industry, and the cost to taxpayers!


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