Drinking water treatment

2000/06/01 Roa Zubia, Guillermo - Elhuyar Zientzia Iturria: Elhuyar aldizkaria

Water supplied by nature

To bring water to our villages and to our homes we must take many steps. Falling water in the form of rain or snow is for us the original water source. This water is collected in the reservoirs, but it is not a mere transport: the water must be cleaned, cared for and potable. Therefore, in the stretch between the reservoir and the municipality water enters the treatment plant.


In the treatment plant, all the large solids that come with water are removed and the first disinfection is carried out. The disinfection is done by ozone, gas that removes bacteria. After entering the water in a chamber, the ozone goes through the water. This treatment consists in the oxidation of certain metals dissolved in water. Then flocculants will be added for collection in the decanting tank

Decanting tank

Liquid separation from small suspended solids is performed here. The water passes through the bottom of the tank and leaves the top. Thus, the solids sink and clean water comes out from above. These tanks have a recirculation system for better decanting.

Sand filter and disinfection

To completely separate solids from water from liquid are filtered. The filter consists of grains of sand of one millimeter in diameter. The water coming out of there is clean and transparent. However, we must add the antibacterial treatment that may appear later. When the water reaches the villages, it has to have certain properties. Therefore, chlorine is added to perform disinfection tasks, fluoride to avoid child dental caries (mandatory addition by law) and adjustment of the pH of soda water.

Central warehouse

Once all these processes have been completed, the water is ready to drink. Therefore, it meets to proceed to the distribution. In addition to the treatment plant, samples are taken in the central warehouse to control quality. These controls allow to adapt the working conditions of the process.


The water extracted from the treatment plant is distributed to both homes and public sources. Samples are taken periodically and used to control the treatment plant. The entire process also depends on the original chemical characteristics of the water. Other types of steps may be alternated, for example, to treat water hardness. It depends on the potability of the water that comes out when opening the source.

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