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The water cycle, learn how to take care of this resource.

Integral Water Cycle

Despite its consumption, the amount of water in the Earth is always the same, but it is in constant movement. Surface water in seas, lakes and rivers evaporates with the warmth of the sun and creates clouds. Rainfall brings the water back to the surface, benefiting Earth’s inhabitants, before the water slowly reach the sea again. The cycle ends here, but it never stops.



Water is a transparent, odourless and flavourless liquid that occupies three quarters of our planet. Water can be found in seas, oceans, rivers, lakes, groundwater, clouds, rains and polar caps. Only 0.64% of this water is fresh and usable (0.62% is groundwater and 0.02% is in the surface water of rivers and lakes). The remaining is seawater (97.2%) or ice (2.16%). The water that we use derives from rivers and groundwater. However, three quarters of our rivers are dirty and polluted. Aware of this fact, CASSA collaborates with several national and international initiatives that work in the recovery of aquifers and improving the environment.




Water is essential for living, because it is part of any living being. Without water, life would not be possible. Sixty-five (65%) of the human body is water. All living beings have water within their structure, but in different proportions according to the species. While a peanut has 3% of water, tomatoes contain 95%.




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Potable water

Usable water is essential for living, and we take it from the rivers basins. In particular for Catalonia, we have three basic supply points. The northeast area of the region covers Ter and Llobregat; both basins are connected and water is transferred to each other.

There are two main actors in the water supply model of most municipalities in Catalonia. On one hand, the public company of the Generalitat of Catalonia Aguas Ter Llobregat (ATLL), which is responsible for the supply at the upper level, capturing and treating the water to make it drinkable for later distribution. On the other hand, local water services companies of each municipality, such as CASSA, purchase water from ATLL, use the water resources available and distribute the water to households for its consumption.


CASSA has been working for several years on environmental awareness, which has been awarded by the International Association of Water Services. One of the concerns of the group is the pollution of rivers, which may have different origins:


To be able to use the water, it must be cleaned and disinfected. Water purification stations are equipped with the most appropriate technologies to conduct the process of cleaning and disinfecting the water of rivers.

CASSA also obtains potable water from groundwater. In this case, this is clean water that is disinfected with chlorine before distribute it to users. The water intended for human consumption is periodically analysed to ensure its optimum conditions for use.



Once the water has its optimal conditions for consumption, it is directed into storage tanks, which stocks large amounts of water in each town. The storage tanks are usually built in elevated places because from there, the water is distributed by gravity through pipes to lower areas where the households are. In these storage tanks, the level of chlorine is always tested. From these tanks, the water is dispatched to households through pipes, which are buried and pass under footpaths. Altogether, it forms a water distribution network.





New sources of water supply: desalination

Our climate in Sabadell is characterised by periods of drought. The current global situation of climate change has led to the research of new sources of drinking water. One of them is seawater that becomes water suitable for human consumption through a process called desalination. This process is already used in some islands where water resources are scarce.


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Wastewater treatment

When we use water, it is unavoidable that it gets dirty. Therefore, before returning the used water to nature, it must be cleaned. The used water, also known as wastewater, runs down the drain into the sewers. Several sewers from different streets come together into a huge sewer called collector, which transports the wastewater to the treatment plant. In this plant, the dirt contained in the wastewater is removed by means of a biological process, and poured clean into the rivers.

CASSA's commitment to the environment means that the company pays special attention to the wastewater treatment and water reuse processes. Treated water cannot be used for direct human consumption, but it can be used to recharge rivers, to irrigate plants or cleaning streets, to extinguish fires, etc.



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Good water use

Water is used in many activities: for personal hygiene; for drinking, cooking, watering plants and providing water to animals; and for cleaning all kinds of things. We use water to play and have fun in the pool and on the beach, or in sports such as water polo, surfing, sailing and swimming. Water is also used to make beautiful springs, to generate electricity in hydropower plants, in industry, to extinguish fires, etc.

But water cannot be manufactured, the amount of water that we have is limited and it must be used appropriately without wasting it. In addition, not everyone has the same amount of water. For example, in Europe, about 200 litres of water per person are used every day; in the US 500 litres are used. In contrast, people in Saudi Arabia only have 5 litres per day for all their activities.

In CASSA, we would like to provide you the following advice that will allow you to save water:


Most people do not realise the amount of water we consume through food. Let’s see if we can help you here.

Large quantities of water are needed to grow or produce the food we eat. All plants and animals need water. Plants and crops can obtain water from clouds in the form of rain. The water they need can also come from hoses and/or irrigation systems. Water is also used to prepare the food you find in the market.

Do you know how much water is needed to produce only one portion of the food you eat?

The following table shows a list of 10 common foodstuff and the amount of water needed to prepare one single serving. Probably the numbers will surprise you!

Discover it!


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    Interesting article with nice and didactic diagrams ! We have to keep in mind the main challenges for the small water cycle (drinking water supply and sanitation): reduce the energy consumption of wa...

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