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The chemical composition of water. Water pollution: physical, chemical, bacteriological. Self-cleaning ability of water sources

The chemical composition of water. In nature, water almost always contains more or less mineral salts dissolved in it. The degree and mineral composition of water is determined by the nature of the soil or soils adjacent to aquifers or surface water sources.

The amount of mineral salts contained in the water is expressed in mg / L.

Organic matter Of these, the most important are substances of animal origin, since they can contain various pathogenic microbes. An indirect hygienic indicator of the presence or absence of these substances in water is the oxidation of water.

Oxidation of water. This is the amount of oxygen (mg) consumed for the complete oxidation of organic substances contained in 1 liter of water (indicated - mg / l). The less organic substances in water, the lower the oxygen consumption for the complete oxidation of organic substances contained in 1 liter of water. For example, the oxidizability of pure groundwater, as a rule, does not exceed 2-4 mg / l, and river water - within 7 mg / l.

One indicator of the possible presence of organic substances in water is the amount of oxygen dissolved in it (mg). 3–6 mg / l of oxygen is dissolved in clean water, and much less in contaminated ones, up to a complete absence.

The presence of ammonia, salts of nitrous and nitric acids indicates a possible water pollution with organic substances of animal origin. Ammonia is a product of the initial stages of decay of organic substances of animal origin, and salts of nitric and nitrous acids are the final products of the mineralization of organic substances. Their presence indicates long-standing water pollution.

The presence of salts of hydrochloric and sulfuric acids in water is an indicator of possible water pollution by animal and human excrement (fecal pollution). Usually in 1 liter of pure natural water contains no more than 20-30 mg of chlorides.

Hardness of water. It is determined by the content of calcium and magnesium salts in it.
There are soft, moderately hard and hard water. Allocate the water hardness - the hardness of raw water, removable hardness, decreasing upon boiling or settling, and unremovable, not decreasing even after boiling water.

Vegetables and meat are poorly digested in hard water, because the proteins in them form insoluble compounds with calcium and magnesium that are not absorbed in the human intestines.

Such water is also not suitable for hygienic procedures: the presence of an excessive amount of salts in it prevents foaming, insoluble compounds settle on the hair and make the washing process difficult.

The hardness of drinking water should not exceed 7 mg / l. This characteristic can also be measured in degrees (1 mg / equiv of water hardness is 2.8 °). Hard water is considered to have more than 20 °, soft - less than 10 °.

Salts of iron. Water containing iron is harmless, but in excessive quantities it gives it a bitter metallic taste and a yellow or yellow-brown color, reducing transparency. In drinking water, up to 0.5 mg / l of iron (in open water) and 1.0 mg / l (in underground sources) are allowed.

Fluorine. Contained in drinking water, it has a significant effect on the condition of the teeth. With its increased concentration, fluorosis occurs (the appearance of dark spots on the tooth enamel), leading to their complete destruction, and with insufficient content, the incidence of caries increases. In the water should be no more than 1.5 mg / l of fluorine, the optimal amount is 0.7-1.0 mg / l. If there is not enough fluorine, water is artificially fluorinated, i.e. sodium fluoride is added.

In natural (land) water bodies, natural self-purification processes take place, if a person does not interfere with this:

* Disinfection with ultraviolet rays;

* Precipitation and sedimentation of suspended particles;

* Oxidation of organic substances due to O2;

* Mineralization of organic residues due to bacteria.
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The chemical composition of water. Water pollution: physical, chemical, bacteriological. Self-cleaning ability of water sources

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