Water represents an existential challenge for Mexico City, which is threatened by both water scarcity and flooding. The solutions lie in its existing natural assets. Reminders come each year when heavy rains bring flooding. At other times water scarcity is a problem and subsidence due to water extraction is ongoing, damaging infrastructure including pipes where 40% of water is lost due to leakage. The metropolitan population of 20 million requires a lot of water and produces a lot of waste. 70% of the water comes from overexploited aquifers and 30% is piped in from increasing distances. In parallel, wastewater (mixed floodwater and sewage) is sent far. All of this is done at great cost and there are fears that the current approach will soon reach its limits. Fortunately, the natural dynamics of its watershed have the potential to solve Mexico City’s water problems. Attention is increasingly focusing on opportunities to conserve, restore, and manage existing ecosystems in ways that ensure their capacity to absorb and filter rainwater and to recharge aquifers, thus mitigating flooding and ensuring sufficient quantity and quality of water.