Roughly 50% of Maine people get their drinking water from public water utilities drawing water from surface water sources (primarily rivers and lakes) and/or groundwater aquifers. Communities that draw water from surface water sources will face new challenges as lakes warm and become increasingly prone to  harmful (toxic) algal blooms, cultural eutrophication and invasive aquatic plant infestations. Each threat poses its own set of challenges, but to understand the role that a warming climate plays in exacerbating these threats as well as the potential interplay between them, it may help to consider a simplified example:

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Soil erosion caused by extreme rain events may result in nutrient rich sediments being washed into the lake.  As sediments build up near shore, new habitat is created for aquatic plant colonization, including invasive aquatic plants. The nutrient-laden runoff helps to spur increased plant growth (both for algae and higher plant forms) in the waterbody. Warmer water temperatures favor blue-green algae or cyanobacteria, and when present in high enough concentrations, cyanobacteria may be toxic to animals, including humans.

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As the increased abundance of plants, algae and associated life forms (such as bacteria) die and decompose, the decayed material that results will break down. When it becomes largely dissolved in the water, it is referred to as Dissolved Organic Matter (DOM).  When DOM in the water supply is treated with chlorine, as it is in some Maine communities, harmful disinfection by-products may form. Drinking water suppliers must strictly limit the concentrations of these harmful by-products in the water supply.  Maintaining these limits in a warming Maine, may be increasingly challenging.

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In addition to the above surface water supply concerns, coastal communities will also have to address ground water supply challenges posed by rising sea levels, such as salt intrusion into the groundwater.