Water pollution occurs when substances dissolved in water exceed its self-cleansing capacity. This happens in many situations: for example, when water, passing through the atmosphere in the form of rain, is enriched with the pollutants it contains (acid rain), or when, flowing over cultivated fields, it washes the chemicals spread by farmers from the fields and carries them into lakes and seas where, together with domestic and sewage effluents that have not been purified beforehand, it contributes to the phenomenon of eutrophication. Toxic substances carried by industrial and municipal effluents also end up in the water, and make a significant contribution to bacterial pollution.

Given the importance of water for life on the planet, it is easy to understand how dangerous water pollution is, endangering the health of people, animals and plants, food production, and environmental balances.

Agricultural pollution

Agricultural pollution originates from the introduction of chemical fertilizers (rich in phosphates and nitrates), pesticides (insecticides and weed killers) and manure from stables in river flows and in the soil. The discharge of chemical fertilizers in rivers, lakes and seas enhances the eutrophication phenomenon. The introduction of pesticides poses the most serious threat as these are not very biodegradable, they deposit and concentrate in river flows destroying all forms of life. A greater attention from agricultural operators could substantially reduce this form of pollution that is particularly dangerous as it can regard also aquifers.

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Industrial pollution
Pollution of industrial origin is caused by the discharge of toxic and non biodegradable substances coming from industrial processing such as cyanides originating from industries producing pesticides and weed killers, cadmium originating from companies producing batteries and accumulators, and chromium as a leftover of plating and tanning industries. Industrial pollution can derive from the discharge of water used in productive processes that contains high amounts of solid dissolved susbstances coming from leaching of solid waste landfills carried out by rainwater or by accidental breaks of tanks and/or pipes transporting very polluting products.

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Thermal pollution

There is also another form of industrial pollution of water that doesn’t regard the content of polluting substances but temperature: thermal pollution. Industries, infact, pour into the sea or into rivers hot water used for their processings. Cooling water is withdrawn from seas, lakes and rivers at a certain temperature and after use is returned at a higher temperature. The temperature rise in water bodies causes the alteration of aquatic ecosystems and the variation of vital processes.

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Domestic pollution

Domestic water pollution is produced by the discharge of domestic sludge containing organic substances and soaps. These substances generally pour into superficial river flows but sometimes reach aquifers. It’s possible to reduce waste water pollution thanks to purification. Discharges are channelled from sewers to treatment stations to abate pollutants before discharging water into rivers and seas. These purification systems, though, aren’t always into force and, moreover, even where discharges are gathered and channelled can occur breaks or inefficies of septic pits, pipes or treatment plants that cause leakage of polluted water.

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Hydrocarbon pollution

It’s caused mainly by accidents on oil platforms and ships used for hydrocarbon transport but also by discharging into the sea of water used to wash tanks of tanker vessels. Crude oil and petroleum products form a waterproof film on water that prevents the exchange of oxygen between atmosphere and water causing damages to marine flora and fauna. Nowadays during transport over sea are used “double-hull” tankers to avoid leaks in case of accidents.

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Oceans have great self-cleansing capacity due to both the composition of seawater and its mass, which often allows effective dilution and oxygenation. But in enclosed seas and along coastlines, the spread of pollutants can cause damage to both the marine ecosystem and human health, so much so that bathing is prohibited in some areas.

The most widespread sources of pollution are discharges (urban and industrial) of organic substances: attacked by oxygen-consuming micro-organisms, this leads to subtraction of oxygen from other marine organisms. In some cases, urban and industrial sewage also contains non-degradable substances, such as heavy metals and radioactive substances, which poison the water causing fish to die.

Sea and ocean pollution

The use of seawater and the exploitation of marine resources may cause serious damages unless they are carried out in a way that guarantees its sustainable use, i.e. that guarantees compatibility between the marine ecosystems and man’s activities. Unfortunately, in many cases, since the antiquity the sea has been wrongly considered as a huge dumping ground in which all waste and dirt could be freely thrown. And it is still considered as such by poorly educated summer tourists, especially those who use sailing or motorboats and throw all their waste into it.

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Heavy metal pollution

The most dangerous are: cadmium, lead, mercury that can be harmful to human health even in very low concentrations, as well as being highly toxic and non-degradable. They accumulate in those organisms that occupy the highest levels in the food pyramid: mercury pollution in the sea provokes the concentration of this metal in fish and the organisms that eat the fish, including men. Mercury that derives from the dumping of industrial waste and that reaches the sea is ever lasting and continues its cycle by passing from one organism to another through the food chain.

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Eutrophication of the sea

Oxygen, light and mineral substances are very important for the sea, as they allow organisms to develop. These nutrients melt into the water and their excessive presence makes the sea particularly rich in organisms. In fact the result is an intense growth of algae and aquatic plants that develop rapidly, altering the balance of the ecosystem. Herbivores that eat algae and plants are not enough and do not manage to control these vegetal populations, that form a large quantity of decomposing material as they die. 

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In many countries to avoid pollution of water of industrial, domestic and agricultural origin in recent years have been introduced more and more restrictive laws that commit companies and public administrations to give particular attention to prevention, control and reduction of water pollution. New technologies and new products have hence been studied and introduced to allow to produce goods and services limiting and eliminating completely water pollution. Also many international organisations, including the European Commission, have dictated a set of simple recommendations for a sustainable management of water resources. Recommendations range from undertaking reforms of institutions that govern water resources to the definition of an adequate price for water to promote a more cautious and less waste-oriented use for water. Sustainable use of water, infact, is based also on waste reduction or its recycling in productive cycles: these practices can increase availability and improve quality of water existing in a given area.

Italian legislation on water

In the ‘70s, with the Legge Merli, was perceived for the first time the exigency to indicate in detail polluting substances posing limits to their discharge into water and their concentration regulating the topic of discharges. The D.P.R. 236/88 is the first example of the enforcement of a Community Directive (Directive 80/778 EEC regarding the quality of water destined for human use) from the Italian State. This law regulates the quality of water destined for human consumption and defines maximum allowable concentration (MAC) and guideline values (GV) for different chemical and microbiological parameters, indicated by the law itself.

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Should water be purified?

Once it’s used, water is returned strongly deteriorated. It contains, infact, many polluting substances (for example leftovers of detergents used to wash dishes or clothes) or other organic substances (for example human excrements). In many countries (unfortunately not all yet) this water is gathered from the sewage system and sent to a purifier that eliminates or reduces at levels compatible with the health of the environment, concentration of polluting substances; water is finally poured again into natural water flows (rivers and lakes) to return into the sea.

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Sustainable management of waste

Possible actions to manage responsibly such an important resource as water could be many, here are some examples. Purification of polluted water is possible to restore a lake, as occurred in Switzerland. If the lake is acidified, for example, immission of carbonates neutralizes acidity of polluting substances…

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