Incorporating climate uncertainty in a cost assessment for new municipal source water

Though new water supply source development has always required planning under many forms of uncertainty, climate change presents an added dimension that may exacerbate supply and water quality challenges. Hence, new decision-support tools are needed, and in this paper an approach that incorporates the uncertainty of climate variability and change into a cost assessment framework for a municipal drinking water provider in Colorado is developed and applied. The water utility provider is developing a new source of water supply, but treatment costs are relatively high because of the advanced processes needed to treat the water to desired standards. Furthermore, the new water source has variable salinity concentrations that are not removed by any of the implemented treatment processes, requiring blending with an existing lower salinity water source. This results in an increase in the finished water salinity (as compared with the existing water source), which can have negative impacts on customer satisfaction and the life span of water-using appliances. To plan for the development of this water supply source, an approach is proposed to assess the potential treatment and residential costs associated with the blending of the new water source with an existing source under climate uncertainty. Uncertainty from climate variability is captured through a previously developed stochastic streamflow and water quality simulation method that utilizes climate change scenarios. Results show that the proposed blend strategies incur increased treatment costs and economic impacts for customers. Specifically, a 30% reduction in annual flows from climate change translates into a 12% treatment cost increase and a 22% rise in residential costs.