Long-term dissolved organic carbon changes in Woronora drinking water system in Australia

Assessing historical records of DOC concentrations (DOC) in drinking water sources is important for water utilities to understand long-term planning for infrastructure needs. This study investigates 15–20 years of historical data of the Woronora water supply catchment in Australia inclusive of the water filtration plant (WFP), the lake from where the water was drawn for WFP supply, and the two primary river inputs. The DOC at each site ranged from 0.8 mg L−1 to 13.9 mg L−1, with the highest and lowest concentrations observed in Waratah Rivulet. The DOC in the lake and WFP significantly (p 0.92; p 73%) of the samples had SUVA254 greater than 2 L mg −1 m-1 in all four sites indicating a dominance of hydrophobic DOC. The terrestrial plant-derived DOC has increased in Lake Woronora, predominantly influenced by historical rainfall magnitude. The results underscore the importance of considering the impact of increased DOC at the treatment plant intake for the planning and operation of the Woronora water supply system. [Display omitted] •Significant increases in DOC and UV254 observed in three of four sites over the last 15–20 years.•Strong correlation found between DOC load and rainfall events.•Predominantly terrestrial plant derived DOC found in the Woronora water system.•Waratah Rivulet identified as the primary contributor of DOC due to higher annual flow.•Study underscores the need for advanced treatment technologies to manage increasing DOC.