The urban world population will increase from 3 to 8.5 thousand million in the 21st century. Cities become hot spots of both demand for water and global food and for disposed used water and nutrients. Sustainability requires that resource flows through our cities are co-managed and connected to agriculture. Reduced use of harmful chemicals in consumer products facilitates treatment to a quality that allows reuse/recycling of water and nutrients. A solid and liquid waste hierarchy can assist in ordering measures. A novel flexible water balance can guide city infrastructure and keep toilet water separate. New water-saving equipment can substantially reduce water use without losing personal comfort. The combination of these new approaches ascertains access to safe urban water, and that recovered nutrients from cities can substitute half of chemical fertilisers needed in food production. Now, thousands of new cities and suburbs provide unique opportunities to develop resource-smart and sustainable flows.

到 21 世纪，世界城市人口将从 3 增加到 85 亿。城市成为水和全球食物需求以及废弃水和养分需求的热点。可持续性要求通过我们城市的资源流动是共同管理的，并与农业相连。减少消费品中有害化学物质的使用有助于处理达到允许水和养分再利用/循环利用的质量。固体和液体废物等级可以帮助排序措施。一种新颖的灵活水平衡可以指导城市基础设施并保持厕所用水分离。新型节水设备可以在不损失个人舒适度的情况下大幅减少用水量。这些新方法的结合可确保获得安全的城市用水，从城市回收的养分可以替代粮食生产所需的一半化肥。现在，数以千计的新城市和郊区为开发资源智能型和可持续流动提供了独特的机会。