Balancing clean water-climate change mitigation tradeoffs

Energy systems support technical solutions fulfilling the United Nations’ Sustainable Development 2 Goal for clean water and sanitation (SDG6), with implications for future energy demands and greenhouse 3 gas emissions. The energy sector is also a large consumer of water, making water efficiency targets in4 grained in SDG6 important constraints for long-term energy planning. Here, we apply a global integrated 5 assessment model to quantify the cost and characteristics of infrastructure pathways balancing SDG6 tar6 gets for water access, scarcity, treatment and efficiency with long-term energy transformations limiting climate warming to 1.5 ◦ 7 C. Under a mid-range human development scenario, we find that approximately 8 1 trillion USD2010 per year is required to close water infrastructure gaps and operate water systems consistent with achieving SDG6 goals by 2030. Adding a 1.5 ◦ 9 C climate policy constraint increases these costs by up to 8 %. In the reverse direction, when the SDG6 targets are added on top of the 1.5 ◦ 10 C policy 11 constraint, the cost to transform and operate energy systems increases 2 to 9 % relative to a baseline 1.5 ◦ 12 C scenario that does not achieve the SDG6 targets by 2030. Cost increases in the SDG6 pathways 13 are due to expanded use of energy-intensive water treatment and costs associated with water conserva14 tion measures in power generation, municipal, manufacturing and agricultural sectors. Combined global spending (capital and operational expenditures) in the integrated SDG6-1.5 ◦ 15 C scenarios to 2030 on water and energy systems increases 92 to 125 % relative to a baseline scenario without 1.5 ◦ 16 C and SDG6 17 constraints. Evaluation of the multi-sectoral policies underscores the importance of water conservation 18 and integrated water-energy planning for avoiding costs from interacting water, energy and climate goals