Technologic resilience assessment of coastal community water and wastewater service options

• Technologic qualitative and quantitative resilience analysis was performed for community water systems.
• Decisions based on past event frequency may over-predict water system resilience.
• No one community water system option considered was most resilient.

The technologic resilience of water and wastewater service options was compared for a coastal community. Options included a centralized, conventional system; decentralized wastewater options such as composting and urine diversion toilets paired with a centralized drinking water system; and centralized drinking water with on-site graywater and rainwater reuse along with a centralized blackwater pressure sewer and digester. Four characteristics of resilience were reviewed based on literature for each option: the robustness, adaptive capacity, rapidity, and resourcefulness. Each system was evaluated for a cold weather event, storm event, power outage, short-term drought, wildfire, and predicted climate changes. Across all events, the service options utilizing graywater reuse and a blackwater pressure sewer and digester were considered the most robust. This was due to the potential advantages of water savings during drought and less environmental contamination during storms, assuming the addition of a backup generator at the household level; however, responsible management of the on-site components of these systems was important for resourcefulness. A scenario with multiple storm, wildfire, and drought events was constructed to quantitatively compare the resilience of the options with respect to water and wastewater service over a 100-year service life. Overall, no one system was the clear resilient choice given the selected events and assumptions, and resilience based on past event frequency over-predicted performance compared to the projected frequency given climate change. Key uncertainties include the duration of event failure, the frequency of future events, and the possible impact of water saving technology on the availability of source water.