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5.7. Pollution of freshwater and saltwater

Water contamination

As a consequence of the different uses of water, the characteristics of the water can change and make it unusable for other uses. The water is then said to be polluted.

The origin of water contaminants can be diverse:

Waste domestic water

Domestic wastewater is the water that is no longer useful in cities and we throw down the drains, such as the one we use in the kitchen, washing, bathroom, etc.

Domestic wastewater contains:

  • Fecal remains, which favor the development of bacteria harmful to health.
  • Detergents.
  • Organic matter, solid substances in suspension, fats, etc. that can produce a bad smell, turbidity, etc.

If the water contains a lot of organic matter, phosphates, nitrates, etc., eutrophication of the water can occur, which causes a large number of microorganisms to develop that need a lot of oxygen to live, decreasing the available oxygen and causing the large number of living beings.

Water pollution from agriculture and livestock

The excessive use of manure and fertilizers in agriculture can cause the infiltrated water to carry these nitrates and phosphates and can cause the eutrophication of lakes and aquifers.

Pesticides, herbicides, and other toxic products used to kill organisms that affect crops, can pass through the food chain to other living beings and cause diseases.

Animal droppings can be used as fertilizer, but when they are excessive they can also contaminate surface and groundwater, as well as causing eutrophication of the water.

Water pollution from industry and mining

The water used in mining and in some industries is loaded with toxic residues, acids, heavy metals, etc. whose treatment is very complicated. They are usually deposited in ponds or deposits that do not pollute the environment.

In power plants (thermal, nuclear, etc.) water is used as a coolant and, although it does not contain toxic substances, since it is hotter than the water from the rivers into which it is discharged, it can alter ecosystems, since it reduces the amount of oxygen dissolved in the water and living beings can die.

Oil slicks caused by accidents (or deliberately) when transporting oil or its derivatives can also cause very serious damage to the environment. For example, the famous case ofPrestige, an oil tanker that in 2002 spilled 63,000 tons of crude oil off the coast of Galicia. The ecosystems of the entire Cantabrian coast were affected for a long time and very intense cleaning and decontamination work was necessary.