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Water is an essential yet scarce resource, crucial for sustaining urban life. Cities worldwide are innovating ways to capture, store, and clean water for consumption and resilience against drought. Aquifers that supply city water are being depleted due to extensive human use, causing cities like Venice, Jakarta, Mexico City, and Miami to sink. To counter this, many cities employ rainwater harvesting techniques, such as rain gardens that capture and filter rainwater back into the soil, gradually recharging aquifers. Some also redirect rainwater from sewer systems to green spaces, enhancing soil absorption and local freshness. Efforts to restore natural water channels, like Madrid’s Manzanares River and Seoul’s Cheonggyecheon River, promote a short water cycle where vegetation increases humidity and rainfall, reduces runoff, and prevents flooding, making cities more resilient to both drought and excess water.
In addition to green solutions, cities maintain grey infrastructure to manage large volumes of water. For example, Barcelona uses underground rainwater tanks to store stormwater and prevent sewer overflow, while Rotterdam has multifunctional public spaces that temporarily hold rainwater for irrigation. Coastal cities in China adopt “sponge city” designs to absorb heavy rains from typhoons. Combining nature-based and engineered solutions—from mangrove restoration to photovoltaic-covered reservoirs—urban areas aim to better withstand extreme weather events, ensuring water security and infrastructure protection amid climate change challenges.
The water crisis suffered by regions of the planet is forcing us to rethink the construction model to make the most of the accumulated water
Water is one of the most precious and, at the same time, scarce resources. Without water, the life that sustains civilization has no place, so cities around the world try to capture it, retain it, clean it for human consumption. Large cities were the first to innovate, but more and more small cities are implementing water collection, storage or cleaning systems. Without seeking to be exhaustive, this article has made a short list of how cities retain water and how cities prevent water from damaging their buildings, using the captured water to improve their resilience in times of drought.
How cities seek to capture water
The aquifers that feed the world’s cities are being emptied as more and more water is used for direct human consumption (drinking, watering to eat, washing) or indirect (cleaning the streets, washing the car, watering golf courses). The cities of Venice and Jakarta are the example that is always set, but Mexico, Miami, Bangkok, Houston and some 200 other cities are sinking due to the emptying of aquifers. It is clear that many water-related activities require ethical judgment in a warming world. But even the cities that use the water best are seeing problems. How to recharge local aquifers?
One strategy is to design rainwater harvesting, for example through a rain garden, a shallow, landscaped depression with native plants that captures, temporarily retains, and filters rainwater back into the ground. They are being used on pavements where the service strip for parking used to be before, as can be seen in Salamanca. Slowly, they recharge aquifers and bring local freshness. In some cities, such as Portland, they have disconnected the downspouts from the sewer system and have redirected it to garden areas or orchards. The key is for the water to spend as much time as possible in the soil.
Renaturation of the environment and short water cycle
Getting water to spend time in the soil is one of the key goals of water conservation strategies. In part, this is why cities such as Madrid or Seoul have partially naturalised channels that were previously contained. Recently, Madrid had contained the Manzanares in a canal now partially restored as a river to which otters have returned and the sediments support trees in the middle of the riverbed, and Seoul had built a highway over the riverbed. the Cheonggyecheon River which has now been removed. London is covering its entire metropolitan perimeter with a ring-shaped perimeter forest. The London metropolitan area has been covered with a perimeter forest called London Green Belt.
All these strategies, in addition to promoting a more natural environment, seek to activate the short local water cycle, that is, vegetation helps with evapotranspiration to increase the humidity of the environment, which in turn acts as a trigger for rainfall. In addition, plant masses help infiltrate rainwater instead of producing large runoff that causes flooding. To a large extent, these new forests are avoiding problems of water accumulation on key dates, as well as accumulating water in the subsoil slowly. In short, cities are now more resilient to excess or lack of water.
In China, especially in its many coastal areas, in order to cope with the floods of typhoons and the torrential release of these when they reach the coast, they are orienting their cities towards an urbanism that they call a sponge city. It is about applying all these techniques and some more to make that the ground absorbs as much water per minute as possible in case of rain. All these nature-based solutions obviously have biological limits and do not have to be used to capture water for human use.
New grey infrastructure to retain water
Dams and retaining walls on rivers and beaches are being dismantled to provide green solutions such as mangroves or wooded banks, because green infrastructure works much better than gray infrastructure to avoid the risks of water accumulation: floods, floods, tides. However, what happens if you are looking to retain a large amount of water for later use? And if you want to preserve it? This is where grey infrastructure still has a place.
The city of Barcelona has under its surface a series of rainwater tanks capable of containing the water of 22 Olympic swimming pools. These are huge rooms full of columns, a set of chambers capable of storing a good part of the storm as it passes through the city. The goal? That the water does not run through the streets or saturate the sewer network, returning fecal remains to the surface. With storm tanks, such as those that they are also seen in Madrid, the city can face large waterspouts, but also take advantage of that water to later use it.
The city of Rotterdam, in the Netherlands, an environment accustomed to fighting flooding continuously, has been installing bowl-shaped squares characterized by hosting sports and leisure uses for some time. For example, Benthemplein Square, where it is possible to play a match. When it rains, this square acts as a huge open-air reservoir, and is filled with water that does not run through the streets of the city. That water is then used for irrigation.
Municipalities around the world seek to conserve water and, at the same time, ensure that its accumulation does not damage urban infrastructure. Some solutions are technologically ingenious, such as covering reservoirs with
