Climate-Driven Increases in Source Water Natural Organic Matter: Implications for the Sustainability of Drinking Water Treatment

Abstract

This study presents an updated analysis spanning over two decades (1999-2023) of climate, water quality, and operational data from two drinking water facilities in Atlantic Canada that previously experienced gradual increases in the natural organic matter (NOM) concentration and brownification. The goal was to assess the impact of recent extreme weather events on acute NOM concentration increases and drinking water treatment processes. In 2023, a dry spring combined with a warm and wet summer caused NOM in the water supplies to increase by >67% (as measured by color). To mitigate increased NOM concentration, the alum dose nearly doubled in 2023 compared to that in 2022. Disinfection byproducts were elevated following the event but remained within the compliance levels. From 1999 to 2023, the two plants responded to gradual climate change impacts and brownification, with alum dose increases of between 4.1 and 8.3 times. Equivalent CO₂ emissions were estimated for alum usage, which increased by 3 to 7-fold in 2023 compared to when the plants were commissioned decades prior. The plants were not only adversely impacted by climate change but also contributed to the global CO₂ burden. Thus, a paradigm shift toward sustainable alternatives for NOM removal is required in the water sector, and climate change adaptation and mitigation principles are urgently needed.

Keywords: brownification; climate change; drinking water treatment; natural organic matter; sustainable development goals.

Figure 1

Percentile distribution of daily precipitation (a) and total monthly precipitation (b) for the study area since 1999. Years 2007–2008 excluded due to incomplete data for these years.

Figure 2

Number of days where the mean temperature was above 20 °C the entire year (a) and for May to September (b) for the study area since 1999. Years 2007–2008 excluded due to incomplete data for these years. Note that there were no days above 20 °C in April.

Figure 3

Time series (a) and percentile distribution (b) of daily lake color for Lake A and Lake B since 1999.

Figure 4

Cumulative alum consumption at Plant A and Plant B (calculated based on raw water flow) since 1999. Note that Plant A only has data beginning in 2003, and data for Plant B were unavailable from 2016 to 2018.

Figure 5

DBP data for compliance samples collected from distribution systems fed by Plant A and Plant B. Samples were collected quarterly (February, May, August, and November) for TTHMs (n = 11 Plant A, n = 7 Plant B) and HAA5s (n = 9 Plant A, n = 5 Plant B).