Water loop

Today, water shortage is becoming a worldwide problem. Big cities from time to time face water scarcity especially during hot summer periods. Water consumption per capita has tended to lessen since 1995, however it is still not enough to have sufficient reserves. In 2008 in Barcelona water in reservoirs dropped below 18% of capacity and that water was not drinkable anymore. City council had to bring drinkable water from Tarragona. This example illustrates that water management in our cities has to be revised to avoid that kind of issue in the future.

 One of the approaches to decrease consumption could be paying more attention to recycled water. Recycling represents only 5% from all water sources. There are some problems associated with recycling. First of all, all treatment plants that we have in cities today are centralized, so we spend a lot of energy on transporting waste water back and forth. 

Another issue that cities have to tackle in order to become sustainable is the urban heat island effect and its consequences. Microclimate control is not easy and needs many things to be considered.  As the microclimate depends mainly on temperature, atmospheric pressure, relative humidity and wind velocity, influencing some of them could become difficult in terms of design and technologies. So, it requires additional resources and could provide extra expenditures for the city budget. 

This project is an effort to rethink water usage and find an alternative way to treat water. The aim is to benefit microclimate conditions in 28 blocks of Poblenou by using decentralized water treatment plants.  

UTCI. 28 blocks.


In order to achieve comfortable environmental conditions we need a huge amount of cold water. That water if taken from the main water supply will affect habitants’s water bills. So, alternative water resources are considered in this project. The annual report states that the average water demand in Barcelona is around 106 liters per capita per day. 61% of consumed water is gray that comes from the kitchen and bathroom sink. That grey water can easily be treated and used for our purpose.  Treated grey water will serve as the main tool to decrease air temperature. There are three main implementations of treated water proposed in this project. Street level, roof level and ground (open spaces) level are three focuses. Firstly, water will be used to irrigate rooftop gardens in order to maintain its capability to defend buildings from surplus of solar radiation. Secondly, facade evaporative cooling system panels will use treated water on street level to provide people with cooled air. Third applications are umbrellas with sprinkles and adaptive ponds with cool water that during evaporation will reduce air temperature. All these three strategies will allow us to establish a comfortable environment and therefore reduce urban heat island.


In order to understand how much grey water we can get we first of all should know  how much we consume. According to Barcelona.cat we know that the 96 millions of cubic meters were consumed by Barcelona’s inhabitants in 2019. The question is how to get consumption of only 28 blocks? Here we have to understand population division. Data about population for each block was derived from cartobcn. Now we know that 11284 people live on our site.  In order to identify the number of inhabitants per building we first of all have to know land use on site. Open street map provides data about land use and number of stores and underground levels in each building. This makes only 0.6% from the whole Barcelona population. We assume that the water consumption is represented with the same ratio. So, in 2019 28 blocks consumed 580 000 m3. However this is not only domestic but also commercial industrial and services needs. In this project we were interested only in domestic usage as it performs the highest demand. 66% of the consumption goes to residential purposes that is 38 000 m3 in 2019. We also know that the water consumption depends on the season. The highest water demand we can see in January and October and September is the lowest one. Grey water can be expressed as 61% of all consumed water. The rest goes to black water and 9% is used to irrigation and cooking. 

Another water resource could be gathered rain water. But how to collect it? Rooftops as they have a broad surface coverage could become the main collectors. By using google maps we observed roofs of all buildings in 28 blocks and identified those that can be useful. We were interested in flat and empty ones. The total area of appropriate roofs is 12 000m2. The amount of rain water that can be gathered depends on precipitation.  The average for Barcelona is 660mm per year. Of course, it varies from month to month . So the highest volume that we can achieve is 10 890 m3 /month  (90 mm/month) in October. 

Implementation of decentralized treatment systems require additional space. As a reference we took an experience of decentralized urban grey water treatment in Klosterenga, Oslo. That approach uses a septic tank, aerobic filter underground and a small wetland constructed on the courtyard. In our proposal wetland was replaced with a nutrients removal tank as it provides the same function. According to the Klosterenga experience area required to construct that kind of system is 1m2 per capita. In order to accommodate treatment plants we observed buildings with underground levels. Some buildings don’t possess enough area to set treatment plants, so they will rely on others. After this 8 constructions were identified as appropriate to play a role of treatment plant holders and to serve others.  

After implementation of the new system all grey water will go to the underground treatment plant and after that will be used to improve microclimate conditions.

Population. 28 blocks.


Basements. 28 blocks.


Treatment plants.


As we already said, influencing all parameters  that create microclimate conditions is almost impossible. In this project we focused mostly on reducing temperature. In order to measure the impact we appealed to UTCI (Universal Thermal Comfort Index). The method that can be applied to reduce temperature is evaporative cooling. However, relative humidity in Barcelona is already high, around 70-75% average. So, adding more humidity by evaporating could have a negative impact. To achieve the goal of influencing microclimate on three different levels three tools are proposed. 

Street level

Streets are those places where we are usually exposed to solar radiation. Moreover, close building location also adds heat to this level. The tool that is proposed to improve thermal comfort on streets is an evaporative cooling system. That cooling system works very similar to air conditioning. In order to avoid adding humidity two steps of evaporating cooling are included. The first one is indirect cooling that uses treated water as a heat exchanger. Small fans will pull hot air from the street, send it through pipes with cooler water and then send it to the second stage. Here partially cooled air will go through pads that are moistened with small nozzles. After all these processes fans will blow cold air back to the street. The temperature reduction mainly depends on the difference in temperature between intake air and water. Evaporative cooling systems will be represented with panels attached to the facades. The amount of water required to supply one panel is 1.1 liter. We assume that ecs. will operate during the most hot hour per day that is from 12 to 5 pm. So, during 1 day of operation one panel spends 5,6 liters of treated water. These panels are one meter long and will be installed only on those facades where streets are mostly exposed to solar radiation. In order to identify those facades we extracted the hottest areas on the street by using a solar radiation map. So, facades(5.4 km) that are closest to those hottest points will hold ecs. As one panel is one meter long we will need 5400 panels and the water consumption of all per one day will become 30m3

Street level ECS.

Evaporative cooling system.

Ground level

Unbuilt spaces that are a lot in 28 blocks were separated into 4 categories: private parks, public parks, unused spaces and parking lots. This project is focused more on unused spaces and parkings as parks are already designed and sometimes not accessible to  intervene. The summarized area of interest is 120 000 m2.  All these spaces were separated into those that are less than 1000m2 and more than 1000m2

To influence microclimate on ground level we proposed three tools. First one is adaptive ponds. During the sunny dry weather these ponds will be used as play or sport grounds.so, we will have  public spaces as an added value. Their position will be 10 cm below average ground surface in order to collect rainwater. After massive rainstorm playgrounds will become a sunken plaza for several days and create a natural pool. Pools will evaporate slowly  and provide inhabitants with additional cooling effects. After some days water from the pool will be sent to the treatment system and serve for the same purpose.   Second tool is inverted umbrellas. They are equipped with 18 small nozzles on the perimeter. Every 5 minutes nozzles spray cool treated water that affects climate. Moreover umbrellas create shaded areas that also contribute to improving the environment. One umbrella consumes 273 liters/day. So, water demand s depends on design and number of umbrellas. Another influential tool is trees. We all know that trees cool the air. Amount of green areas in 28 blocks today is 8m2/capita. The goal of Barcelona city council is to increase it by 15m2./capita. Using trees as a design proposal can help us to achieve both goals. Moreover, trees doesn’t require water to irrigate and provide shade. These 3 main tools will be implemented for ‘big’ and ‘small’ areas respectively. Combination of umbrellas and ponds are designed to fill ‘big’ areas, and umbrellas and trees will be used for ‘small’.

Unbuilt spaces.


Adaptive ponds.


Vegetation. 28 blocks.

Roof level

Available roofs that were mentioned above are proposed to be turned into rooftop gardens. Vegetation on the roof protects buildings from extra heat and reduces electricity bills by decreasing operation hours of air conditioners inside. There are several types of plants that could be implemented. Perennials shrubs and grasses are prevailing. Grass will be exposed to solar radiation a lot, so the  roof definitely requires additional irrigation to keep plants alive and efficient. 1m2 needs 96 liters of water per month. If all available roofs will be plated we need 11 600m3 of treated water. After implementation of this proposal roofs in 28 blocks will attract more people and serve as additional public space. 

Available roofs. 28 blocks.


Rooftop gardens.

Water requirements for 3 tools.

System effectiveness.

Internet of buildings.


Using treated water and special tools can help us to make small changes and improve the urban environment. UTCI that was calculated after implementing an extreme design proposal ( all three levels are fully equipped) illustrates an increase in no thermal stress index areas by 3.6%. That means that more areas turn from strong  heat stress index to no thermal stress index. At the same time, water is required to feed these tools much less than all treated water that we can get. Calculations were made for august as the hottest month. Treated grey and rainwater  can achieve 24 000 m2 and the required is only 13 000m3. That means that extra water can be collected and make a reserve  for the future. Another alternative is that water can also be used for technical purposes and for residential needs. Treated water alone cannot meet residential demand but in periods of water shortages it will cover 85% of residential demand. In addition, new public spaces and ecosystems will appear in 28 blocks.  Rethinking water may provide millions of alternatives and an effort to improve urban microclimate could be one of them.


Extreme scenario.

UTCI. 28 blocks.

UTCI. Extreme scenario impact.

Effectiveness of extreme scenario.



  1. Z.A. Rashid, Syed Abdul Mutalib Al Junid. ( 2014).Trees’ cooling effect on surrounding air temperature monitoring system: Implementation and observation.
  2. Petter D. Jenssen. (2004).Decentralized urban greywater treatment at Klosterenga Oslo. 
  3. (2019).Barcelona green Infrastructure and biodiversity plan 2020.
  4. Jan Vymazal.(2010). Constructed Wetlands for Wastewater Treatment.
  5. Sara Wilkinson & Tim Dixon.(2016). Green roof retrofit. Building urban resilience.
  6. Barbara Imhof & Joëlle Mühlemann.(2005). Greywater Treatment On Household level In Developing Countries A State Of The Art Review.
  7. Günter Gross.(2017). Some effects of water bodies on the n environment – numerical experiments.
  8. Ruzana Sanusi, Denise Margaret  Johnstone, Peter B May, Stephen J. Livesley.(2017).Microclimate benefits that different street tree species provide to sidewalk pedestrians relate to differences in Plant Area Index.
  9. Sam C M Hui, W Y Cheung.(2009). Two-stage evaporative cooling systems in hot and humid climate.
  10. Cascadia Green Building Council. (2011). Toward Net Zero Water: Best Management Practices For Decentralized Sourcing And Treatment.

WATER LOOP is a project of IAAC, Institute for Advanced Architecture of Catalonia
developed at  Master in City and Technology in 2019 by:
Students: Jianne Libunao, Linara Salikhova, Rashid Gilfanov
Faculty: Areti Markopoulou, Alex Mademochoritis and Iacopo Neri.