8. Mexico City

Water shortages are nothing new for many of the 21 million inhabitants of the Mexican capital.

One in five get just a few hours from their taps a week and another 20% have running water for just part of the day.

The city imports as much as 40% of its water from distant sources but has no large-scale operation for recycling wastewater. Water losses because of problems in the pipe network are also estimated at 40%.

9. London

Of all the cities in the world, London is not the first that springs to mind when one thinks of water shortages.

The reality is very different. With an average annual rainfall of about 600mm (less than the Paris average and only about half that of New York), London draws 80% of its water from rivers (the Thames and Lea).

According to the Greater London Authority, the city is pushing close to capacity and is likely to have supply problems by 2025 and "serious shortages" by 2040.

It looks likely that hosepipe bans could become more common in the future.

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10. Tokyo

The Japanese capital enjoys precipitation levels similar to that of Seattle on the US west coast, which has a reputation for rain. Rainfall, however, is concentrated during just four months of the year.

That water needs to be collected, as a drier-than-expected rainy season could lead to a drought. At least 750 private and public buildings in Tokyo have rainwater collection and utilisation systems.

Home to more than 30 million people, Tokyo has a water system that depends 70% on surface water (rivers, lakes, and melted snow).

Recent investment in the pipeline infrastructure aims also to reduce waste by leakage to only 3% in the near future.

11. Miami

The US state of Florida is among the five US states most hit by rain every year. However, there is a crisis brewing in its most famous city, Miami.

An early 20th Century project to drain nearby swamps had an unforeseen result; water from the Atlantic Ocean contaminated the Biscayne Aquifer, the city's main source of fresh water.