Protecting Our Water: New Insights into Wildfire Ash and Reservoir Health

Rob Beeson
Jan 12
3 min read

Approximately 70% of the UK’s drinking water coming from upland catchments, so the link between the health of our moorlands and the water in our taps is undeniable.

Recent scientific research has shed new light on a critical threat to this water supply: wildfire ash. A new Canadian study, published by researchers at the University of Waterloo and University of Alberta, digs deep into what happens when ash from fires enters our reservoirs and rivers.

For those of us dedicated to land stewardship and rural conservation, understanding this science is vital. It reinforces why managing vegetation and preventing catastrophic wildfires is not just about protecting grouse or heather - it is about securing clean drinking water for millions. Annual water industry losses from wildfires in the UK are estimated to be £16 million.

The "Ash Tea" Effect

When a wildfire burns across a landscape, it leaves behind ash. When rain falls, this ash mixes with surface water, acting much like tea leaves steeping in a pot. The study focused on the organic carbon that dissolves from the ash into the water - a process scientists call leaching.

This dissolved organic carbon is a headache for water companies. When water rich in organic carbon goes through the treatment process (specifically chlorination), it can react to form "disinfection by-products" (DBPs). Removing these requires expensive, complex treatment to ensure the water is safe to drink.

Key Findings: The First 24 Hours Are Critical

The researchers discovered that the way scientists have traditionally tested ash in the lab might be leading to inconsistent results. By testing ash from four different wildfires they found that time is a crucial factor.

The 24-Hour Spike: The concentration of dissolved organic carbon changed significantly within the first 24 hours of ash mixing with water.
Tripling of Treatment Risks: Crucially, the study found that when ash remains in water for 24 hours, the release of materials that form harmful chemical by-products nearly triples compared to a brief 30-minute mix.

This suggests that if heavy rain flushes ash into a reservoir where it sits and mixes, the impact on water quality could be far more severe than rapid runoff models might predict.

Not All Ash Is Created Equal

One of the study's most interesting findings for land managers challenges the "common sense" view of ash appearance. Typically, it was thought that white ash (indicating high heat and complete combustion) would contain less organic matter than black, char-like ash.

However, the study found that this isn't always true. In fact, lighter-coloured ash samples (often assumed to be 'cleaner') released some of the highest concentrations of organic carbon in this study. The organic matter content in the ash samples ranged from 3.7% to 21%, but the visual appearance of the ash was not a reliable indicator of how much carbon it would release into the water.

Why This Matters for Moorland Management

Why does a study on water chemistry matter to a gamekeeper or a hill farmer? Because it validates the importance of what we do.

Prevention is Better than Cure: The study confirms that ash introduces complex challenges to water treatment. The most effective way to protect water quality is to prevent high-intensity, damaging wildfires in the first place.
The Role of Management: Traditional land stewardship, including the management of fuel loads, is essential. By reducing the volume of vegetation available to burn, we reduce the intensity of potential wildfires and the sheer volume of ash that could end up in our rivers.
Accurate Science: The paper argues for better, more standardized testing methods. We support this. Accurate data helps water companies plan, and it helps land managers understand the true value of their conservation work in mitigating these risks.

Looking Ahead

As climate change increases the risk of drier summers, the threat of wildfire grows. This research serves as a timely reminder that the health of our uplands is directly connected to the health of our communities. By continuing our traditional role as custodians of the land, managing fuel loads responsibly, and working with water companies, we can help ensure that the water flowing from our moors remains clean and safe.

Takeaway

Preventing severe wildfires through active land management is the single most effective way to stop harmful ash from contaminating the drinking water supplies that millions of people rely on.