Chapter 5 emphasizes the need for adaptation and mitigation specifically for water systems in cities. It depicts how the water system and treatment greatly depend on the situation of the city by exemplifying water system of four very different cities — New York City, Mexico City, Lagos, and Santiago de Chile. These cities’ water systems show high contrast to each other. For instance, New York City has a developed water system while Lagos doesn’t have a particular wastewater treatment to depend on. Cities like Lagos and Santiago de Chile are facing a crisis in water supply and treatment. The water system can be regulated by either the government of the city or by informal groups. Cities that rely on informal groups for water treatment are limited to money and resources, and thus, these cities struggle in obtaining safe water. As in mitigation, reducing greenhouse gases is a crucial step for facing water system crisis due to climate change. Using less water is one way to mitigate the water system problem. In addition to less water, there are various potential ways to mitigate this obstacle, from reclamation and recycling to establishing water marketing. Furthermore, there are city policies that must be considered pertaining to water treatment. Cities such as Chicago, London, New York, Seattle, and Toronto encourages adaptation and mitigation for the urban and regional water crisis.