These challenges have been further elaborated in the context of disadvantaged groups in urban and rural settings (Chapters 6-7), for refugees and forcibly displaced populations (Chapter 8), and across different regions (Chapter 9). The first relates to water supply, which corresponds to the volumes of water that can be withdrawn sustainably from surface and sub-surface sources, as well as from unconventional sources. This includes desalination of sea water, water reuse and recycling, and rainwater and fog harvesting.