Mexico City is located at the bottom of the Basin of Mexico in the central plateau of Mexico. The surrounding mountain range created the shallow lakes during the rainy season. The Aztecs settled in this area in 14th century and constructed dikes to protect their capital city, Tenochitlan. After the Spanish conquest, flooding continued to be a threat to the city. Since then. the rivers have been diverted from the Basin of Mexico and lakes now cover only one one-hundreth of the original area. Drainage canals and dams were built to prevent flash flooding. These enormous (and expensive) efforts have been paid to keep Mexico City dry.

After hearing all of this, you might have a hard time understanding that the city is also actually short of water. In order to quench the thirst of this city of [more than] 20 million inhabitants, groundwater has been extracted more than twice fast as the replenishment rate. As a result, Mexico City is sinking, which could be as bad as 40 cm/year. Even with this rate of extraction, it is not enough to meet the water demand for this mega-city. The water distribution system of the Mexico City is old and it is also heavily damaged by sinking. It is estimated that 40% of the potable water is lost somewhere in the distribution system before reaching the city's water taps. (For comparison, the water loss rate for Los Angeles is 9% and 3.6% for Tokyo.) The other issue is the way people use water in the Mexico City. People in Mexico City, on average, use 300L of water a day. This is twice as high as in European countries, due to the low adaption of water efficiency measures such as low flush toilets.