How Forest Fires May Affect Water Quality

​Forested areas account for a substantial portion of the water supplying the population in North America.

The effects of wildfires pose significant risks to water supplies, often compromising the ability of water systems to deliver safe drinking water to the public.

A large portion of water in California comes from the Colorado River, and when wildfires rage in forested watersheds, the potential impacts on water supplies, water quality and overall stream health extend far downstream and continue for years.

The various water utilities work to make water supplies safe, but they don’t always succeed.

The Canadian Water Network recently delivered a report with the Water Research Foundation on the effects of wildfires on water supplies. It contained information homeowners should know.

Key messages from the report:

• Wildfires in forested regions are associated with negative impacts on drinking water source quality.
• After wildfire, the timing and magnitude of precipitation events (rainstorm or snowmelt) are key factors driving changes in water quality, making effects more variable and difficult to predict
• The short-term broadly ranging fluctuations in water quality that may often be anticipated after severe wildfire can constitute a major challenge for drinking water treatment, because source water quality often exceeds existing treatment and/or operational capacities.
• Drinking water source quality can be negatively impacted for variable durations after wildfire (short-term impacts lasting months to years, or long-term impacts lasting years to decades), necessitating additional and costly treatment capacity (infrastructure and/or operational) beyond that required prior to wildfire.
• Water treatment plants and processes are not always designed to treat the range of changes in the character and/or magnitude of source water quality (like dissolved organic carbon, nutrients or heavy metals) after wildfire, and some of these fluctuations may render existing treatment capacity inadequate.
• Mitigation of the impacts of wildfire on drinking water supplies requires a three-pronged approach that includes:

1. Assessment of wildfire risks based on the potential to impact the desired values for protection, which includes drinking water supplies as a consideration.
2. Strategic fuel management for the protection of source water supplies.
3. Drinking water supplier preparedness (i.e., enhancements to infrastructure).