O&M labor costs were based on the maintenance activity schedules provided by each design team, and labor wages were assigned based on the skill level required (e.g., construction, electrician). O&M replacement parts were included to account for part lifetimes less than the total system lifetime (e.g., pumps, batteries, solar panels), and consumable costs accounted for any chemicals and materials used within the system (e.g., zeolite, LPG, GAC). Electricity costs were estimated based on the electricity needs reported by each design team and the global average electricity cost per kilowatt-hour. Each system expense or revenue was resolved to its equivalent annual worth, and total cost of each system were normalized to a daily per capita basis (i.e., U.S.