Purification Treatments

What does potable water mean? Water is considered potable (safe to drink) only when it contains no germs or bacteria that can be harmful to our health (i.e. it is microbiologically pure), when the content of chemicals does not exceed legal limits and when it is clear and has a pleasant smell and flavour. However, not all fresh water present in nature can be used directly for human consumption. Water, in fact, can contain certain substances acquired at its origin which make it “non-potable”: some come from the ground it has filtered through, others are due to pollution. For these reasons, some waters have to be purified. Water treatments can be more or less complex. In general, groundwater only requires disinfection, which guarantees the elimination of potentially harmful microorganisms throughout the distribution network, whereas surface water, which is more vulnerable to pollution, must undergo more complex treatments carried out in large treatment plants. Therefore, before the water reaches our taps, it must follow a specific pathway that can include one or more of the following steps:

Coagulation and flocculation: the water may be turbid due to the presence of suspended solids. A substance called a coagulant is added, which attracts the particles like a magnet, to form flakes called flocs.
Sedimentation: the water “rests” at the top of a tank where the floc, due to its weight, sinks to the bottom, thus “clarifying” the water.
Sand filtration: the water flows into tanks full of sand, filtering it and withholding any particles still present.
Activated carbon filtration: this eliminates certain types of pollutants and substances that can alter the taste and smell of the water.
Disinfection: this destroys any germs and bacteria. There are several disinfection methods: a disinfecting substance can be added (such as chlorine and its derivatives or ozone), water can be subjected to ultraviolet radiation which destroys microbes or it can be filtered through membranes with tiny pores that block the microorganisms.