A delay in bringing a powdered activated carbon (PAC) dosing system into service has been identified as the cause of a serious taste and odour incident affecting consumers supplied by Glenfarg Water Treatment Works in Scotland.
The Drinking Water Quality Regulator for Scotland (DWQR) classified the incident as serious after consumers reported an earthy and musty taste and odour in their drinking water.
Geosmin Causes Taste and Odour Complaints
Between 29 May and 5 June 2026, Scottish Water received 62 contacts from consumers supplied by Glenfarg Water Treatment Works. Of these, 56 related to reports of an earthy or musty taste and/or odour.
An investigation identified elevated concentrations of geosmin as the cause of the complaints.
Fifteen samples collected from final water and consumers’ taps recorded geosmin concentrations above the recognised taste and odour threshold of 3 ng/l.
Geosmin is a naturally occurring compound associated with earthy and musty tastes and odours in drinking water.
PAC System Was Not in Operation
The increased geosmin levels originated from Glenfarg Reservoir, which supplies the Glenfarg Water Treatment Works.
Although the treatment works is equipped with a powdered activated carbon dosing system designed to remove organic compounds such as geosmin, the PAC system was not operating when the incident occurred.
As a result, the elevated concentrations were not effectively removed during the treatment process, leading to an impact on the quality of the treated water.
DWQR attributed the incident to a delay in bringing the PAC dosing process into service.
Corrective Actions Underway
Following the incident, Scottish Water identified four actions to address the issues highlighted by the investigation.
DWQR has accepted the proposed actions as appropriate and will monitor their completion before formally signing off the incident.
The incident highlights the importance of ensuring that critical water-treatment dosing systems are operational and available when changing raw-water conditions require additional treatment.
For water utilities, reliable operation and timely commissioning of treatment equipment remain essential for maintaining consistent drinking-water quality and responding effectively to naturally occurring contaminants.
