Purification processes are carried out to ensure that wateris compliant with the established requisites for drinking, and to improve its organoleptic (colour, odour, taste), chemical (e.g. removal of iron and manganese) and microbiological (e.g. disinfection of water to eliminate Escherichia coli) characteristics.
The main purification treatments are, in sequence, the following.
Water that is of higher quality at source, such as those from springs or deep wells, generally require simple treatment (e.g. sedimentation, filtration and disinfection). This is because they benefit from natural “self-purification” processes that occur during filtration in the ground and subsoil layers. Surface waters and some aquifer waters, especially on the plains, require - on account of their characteristics and vulnerability to accidental pollutant spillage - complex treatment that generally includes many or all of the above-described stages. In some aquifers it's necessary to remove naturally occurring contaminants such as ammonium, iron and manganese or anthropic pollutants, the most common of which are organohalogenated compounds.
Disinfection is an indispensable part of the treatment process as it ensures adequate health safety. Adding chlorine-based disinfectant at both the water production plant and along the distribution network ensures potentially pathogenic micro-organisms are removed at source and prevented from spreading along the network. The introduction of chlorination in the early 20th century, together with filtration, drastically reduced the spread of illnesses carried in drinking water all over the globe. The odour and taste caused by the presence of chlorine can be removed very simply: just leave the water in a jug so that the chlorine evaporates naturally. Water, since it has a more pleasant taste at lower temperatures, is best drunk cool.