Visiting Aigües de Barcelona water treatment plant

Visiting Aigües de Barcelona water treatment plant

On the 15th of March TAPP Water’s team was lucky enough to do a visit to one of Aigües de Barcelona water treatment plants. Aigües de Barcelona is the company that manages the water supply of all homes in the city of Barcelona, and they have one of the most complex and advanced water treatment plant in Europe, as well as a history of over 150 years. Also read our other article about "if you can drink the tap water in Barcelona". Here's a summary from our visit:

About the Barcelona water treatment plant

The ETAP (Estación de Tratamiento de Agua Potable / Drinkable Water Treatment Plant) of Sant Joan d’Espí was built approximately 50 years ago, in 1955, when the population of Barcelona started to demand more water. Until that point in time, water was being extracted from two aquifers from rivers Besòs and Llobregat. When we did the visit to the facilities of Aigües de Barcelona, we could see how the different processes the water needs to go through in order to go from the muddy water coming from river Llobregat to a completely clear and drinkable water, without a trace of the initial smell and color that the water had came in. When you see it first hand, it really feels like magic.

Where does Barcelona tap water come from?

Aigües de Barcelona actually uses water coming from different sources. As we mentioned before, river Llobregat is the main source of water supply of the city, but it is not the only one. Water is also being sourced from river Ter, and a small percentage from the river Besòs as well as the aquifers formed around the river Llobregat and Besòs. The water from the aquifers is in any case used in small amounts in order to avoid their salinization due to their proximity to the sea. A desalinization plant is used when there is a really high demand or periods of extreme drought. This plant was installed in 2009. Aigües de Barcelona manages to supply water to 24 different municipalities and can produce 450 thousand cubic meters of water per day. They manage to treat water at a speed of 5,3 cubic meters per second. The figures are really difficult to imagine until you don’t see live the amount of water moving, being treated and transported through all types of engineering mechanisms.

How is the water treated before it arrives to your home?

The depuration process is somewhat complex, especially if we need to mention technical aspects such as chemical compounds, mechanisms, technologies, etc. That is why we have elaborated a small summary where, dividing all the different phases of the purifying process, we want to explain you the key parts of it: Visiting Aigües de Barcelona water treatment plant 1.Water capture: Water is extracted from the river and is transported to the silting chambers. 2.Silting: Stones and sand are separated from the water. 3.First elevation: Water is elevated 11 meters so that the process can continue. 4.Dosification of reactives and initial disinfection: Chlorine dioxide is added to the water to oxidize the iron and magnesium. Another compound is also added to make the particles flocculate and deposit at the bottom of the tanks. 5.Decantation: The particles of mud are deposited at the bottom of the tanks and the clarified water stays at the upper part. 6.Sand filtration: The water goes through a filter with sand particles that absorb other solids that might be still present in the water after decantation. 7.Second elevation: Water is separated through big Archimedes screws to be processed afterwards. Part of it will go through an ozone and activated carbon process and the rest through ultrafiltration, osmosis and remineralization. Here the water separated in two different buildings: 8.Ozonation (PROCESS A): Ozone eliminates and helps the precipitation of certain organic compounds and microorganisms, making it easier to take them out of the water through activated carbon filters. 9.Filtration through Granular Activated Carbon (PROCESS A): The GAC eliminates the rest of the organic compounds still present in the water as well and retains the metallic oxide. 10.Ultrafiltration (PROCESS B): It is a necessary filtration so that the semipermeable membranes of the reverse osmosis that will take place later do not break or get saturated too soon. This ultrafiltration does not allow the entrance of bacteria but some virus might still remain. 11.Reverse osmosis (PROCESS B): Osmosis is a total barrier to virus and bacteria and eliminates almost all the minerals and salts of water. 12.Remineralization (PROCESS B): Water is re-mineralized through carbonated rocks to make it less corrosive. 13.Deposits of treated water (A + B ARE MIXED AGAIN): Water that has been through process A is mixed with water that has been through process B. 14.Stabilization and post-chlorination: A final chlorination of water is performed to ensure that water arrived to every home safe, without getting infected in the distribution process. 15.Final pumping: Water is pumped to all the different points from which it will be distributed to the final consumers.

How can the tap water differ in taste depending on area?

Even if the water passes through the same water depuration process in Sant Joan d’Espí, the origin of the water, time of year and potentially even local water pipes in Barcelona can impact the the taste of the water (milder, stronger or more chlorinated flavor). For example, water coming from the Llobregat and the Besòs rivers have a higher percentage of salts and contaminants, so its treatment might need higher levels of disinfectants like chlorine, while the one coming from the Ter and the aquifers have better organoleptic properties.


Overall the visit to the water treatment plant really helped us really understand the process of water treatment for domestic consumption, the functioning of the hydric networks of Barcelona and the origin of the organoleptic characteristics of water in this town and the neighboring municipalities. It was also interesting to understand the high regulations public water has to undergo, as well as the continuous monitoring that is being carried out. Sometimes we take for granted getting fresh and clean water by just opening a tap. We hope this article makes you value your tap water even more!
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