Potabilization
Sources of pure water are rare. To be potable – that is, safe to drink – tap water must undergo a series of decontamination treatments before being delivered to the consumer.
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The water is first passed through grills which remove the larger bits of debris, like leaves, plastic objects, etc.
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Colloidal particles – that is, very fine ones, like clay -- are neutralized via the addition of a metallic salt -- this is called coagulation (…) – then aggregated with the aid of a polymer – this is called flocculation.
The resulting mass, called a floc, is decanted at the bottom of the tank. This is carried out under conditions of slow agitation, in fact much slower than what is shown in the animation.
The smallest particles are removed by filtration with a bed of sand or anthracite that contains bacteria. Why bacteria? So that they can digest the organic particles that they are so fond of.
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At this stage, the odor, taste and color of the water still leave a good deal to be desired: Ozone will take care of this.
In addition, Ozone eliminates pathogenic germs and micropollutants like insecticides.
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A final filtration using activated Carbon removes hydrocarbons and nitrates.
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Finally, the addition of Chlorine will maintain good quality at the microbial level while the water is sent to consumers via reservoirs and pipes. One factory must produce around 100,000 m3 /day to supply 500,000 inhabitants. But having potable tap water does not come easily. Despite the use of leading edge technologies, it can happen that the water is not suitable for drinking.
Production sites are thus sensitive, protected areas, and the water is a resource that is kept under a high level of surveillance.
