Estimating Carbon Emissions in Water Supply Portfolio Evaluations Including Recycled Water and Greywater

Carbon emissions assessments and carbon footprint analysis are becoming more common in water supply planning studies. In most cases analysis are made by defining carbon emissions at the supply option level for large-scale supplies (i.e., conventional water filtration, desalination, etc). After assembling a water supply strategy with a defined portfolio, the carbon emissions of the supply options involved are combined to define the carbon emissions of the portfolio. This approach is less applicable when the supply portfolio includes smaller scale supply options that can be implemented in a decentralized fashion and in many times on-site (building level). Water supply analysis can better capture the real benefits of options when water supply is analyzed as a portfolio in a systemic way. This paper describes the application of a systems model to evaluate the actual use of sources in a portfolio. The model provides the opportunity to estimate effectiveness in the reduction of demand from municipal systems, annual costs savings, and energy use and indirect GHG emissions associated with the sources. Two portfolios are evaluated in two separate cities with large variations in the energy footprint of the municipal system. Comparison will be made on the benefits of the additional sources, and GHG emissions (driven by the current municipal water footprint). The use of a systems tool allows us to better account for the real GHG impacts on water supply portfolio decisions.