Water: origin and treatments
Our water comes from a deep groundwater aquifer, a sort of underground reservoir formed around 100 metres in depth and beyond, when rainwater or water from melting ice meets a waterproof layer of soil. The water of the most superficial groundwater (up to 40-50 metres deep), or non-potable groundwater, on the other hand, is almost never drinkable, but can be used to irrigate fields. The water distributed in taps is collected (i.e., withdrawn) exclusively from the deep groundwater.
In some cases, the water we withdraw undergoes purification treatments, as the rest of the resource comes from groundwater with excellent quality water from a chemical and microbiological point of view that we can use directly, without further treatments. We have two types of water treatment plants:
- Activated charcoal plants: used to treat water where organic compounds such as herbicides or other organic micropollutants of industrial origin are present in the groundwater;
- Oxidation and filtration plants: used to treat water in areas where substances of geological origin are naturally present in the underground groundwater, such as iron, manganese, hydrogen sulphide, ammonia.
The wells are used to withdraw water from the groundwater and we can consider them the modern version of the traditional well that we all know.
Before constructing a well, hydrogeological surveys must be carried out to verify the availability of water in the subsoil, both in terms of quality and quantity.
Subsequently, the soil is drilled to reach one or more groundwater aquifers, located at different depths.
The well basically consists of a hole of variable diameter, between 60 and 100 cm, into which a steel tube with a diameter between 20 and 50 cm is inserted. The water is lifted and pushed to the purification system through a submerged pump if it is to be treated, or directly to the reservoir.
Commonly known as aqueduct towers, the reservoirs are part of the panorama of our territories, which owe so much to the presence of water and the history of its management.
But what are these strange, tall constructions for?
The reservoirs are intended for the temporary storage and subsequent release of water according to the demands of the water system. The reservoir must therefore be able to accumulate, during the lowest consumption hours, the water coming from the pipeline in order to return it during peak hours, thus helping maintain a balance in supply provision. This reservoir function is called “compensation”. It is flanked by the “reserve” function, which allows making a certain volume of water available that can be used in extraordinary situations such as fires, faults or maintenance interventions.
Finally, the reservoir is used to regulate water pressure in the water network: the water reaches homes from the reservoir, at least up to the fourth floor, with only gravity to thank and no need for pumps.
Waste water treatment plants are a complex and articulated system that serves to clean up sewage, i.e., civil waste and some industrial waste from the territory, through the sewer system and inter-municipal trunk lines.
The dirty water is first filtered to free it of smaller and larger solid debris ranging from pieces of wood to the waste that is produced every day (plastic, cotton buds, cigarette butts) and should never be thrown in water or in the toilet.
At a later stage the smaller residues such as sand, soil, oils and greases must be filtered, which will be eliminated by suction.
Only at this point does the actual purification take place, that is, the cleaning from pollutants: oxygen is added to the water to nourish the naturally-present microorganisms that will proceed to eliminate any harmful bacteria and harmful substances.
During their stay in the tanks, the microorganisms tend to join together and form small clusters of typical brown colour, called "activated sludge floc".
The single, very light bacterium manages to float in the water, while the "sludge floc" which is heavier falls to the bottom. This is how we separate clean water from sludge containing pollutants in the separation tanks. The heaviest sludge falling on the bottom is sucked, separated from the water and destined for a new life with a view to circular economy, while the purified water is disinfected and returned clean to the environment or reused for agriculture or civil uses.