Water (H2O) - a colourless, in a layer over 2 m bluish liquid. At 1 ATM temperature boiling point of 100 degrees, the temperature of melting of 0 degrees. Density at 4oC 1,0000.
Chemically pure water does not exist in nature.
Dissolved in natural water usually contains gases, mineral and organic compounds as suspended solids or sludge in the water can be of mineral and organic substances, bacteria, fungi, protozoa , and other plant and animal organisms.
Depending on the content of mineral salts distinguish fresh water (less than 0.1%), mineral (from 0.1 to 5%) and brine (over 5%). Some of mineral water used for medicinal purposes (see mineral water).
Water is an essential constituent part of all living organisms. The amount of water contained in the body of the adult person is about 65-70% of its weight; fluctuations in its content lead to changes in the function of cells and tissues, the loss of 20% moisture causes death. Water in the human body receives a number of biologically essential elements.
Daily need of the human body in water in normal conditions is about 2.5 liters When the temperature of the air and physical work, the demand for water increases.
Hygienic water is very high; a large number of it spent in the sanitary and household purposes.
Water pollution. Natural water polluted with sewage and garbage. Open water reservoirs may be contaminated as directly sanitary and industrial wastewater, and at receipt in waters contaminated groundwater from coastal areas. In epidemiological terms the greatest danger of pollution of water for domestic and fecal sewage and sewage enterprises for raw materials of animal origin (see Sanitary protection of water bodies).
Water as a factor of noncommunicable disease. The composition of groundwater by the chemical composition of soils and rocks that lay on the water. The lack or excess of one or the other trace elements in the soil varies and its content in natural waters, raising conditions for development of mass diseases of the population, the so-called geochemical endemi, the most famous of which is endemic goiter. Drinking water is the main source of intake of fluoride, lack of content in water (below 0.6 mg/l) may cause tooth decay, and excessive (more than 1.5 mg/l) causes endemic fluorosis (see). Water containing more than 10 mg/l nitrogen, nitrates can cause toxic cyanosis (infant methemoglobinemia in infants (see Nitrate). Adversely affects the body's water and very high salinity (e.g. sea). However, its consumption is limited due to the poor organoleptic properties with a high content of chlorides and sulphates of alkaline and alkaline earth metals. Valid hardness of drinking water - not more than 7 mg-EQ. The danger for human health may present water containing various poisonous compounds, including radioactive substances. The source of their revenues into the water can be a waste water of industrial enterprises. It is also possible extraction of groundwater toxic compounds from the soil and bedrock.
Bacteriology of water. Water is a habitat saprophytic bacteria. The number of bacteria in water is determined by the content of organic substances. The largest number of microbes contained in the surface layer of silt open reservoirs (from 100 million to 300 billion per 1 g).
The presence of bacteria in the groundwater is determined by the depth of the aquifer: usually the deeper lying underground water, the less they contain bacteria. In some cases there is a significant pollution of deep underground waters, which is explained by the seepage of water without filtering through the cracks and voids in soil and rocks. Composition of the microflora of the water and the soil is very similar. In the silt of fresh reservoirs widespread anaerobic bacteria decomposing fiber, fats, nitrifying, nitrogen-fixing bacteria, actinomyces, fungi, etc.
Water as a factor in the spread of infectious diseases. Pathogenic microbes entering into the water of various pollutants, are not well suited to the conditions of life in the water, so we have to talk not so much about breeding them in water, but about the possibilities for survival.
The life span of pathogenic bacteria in water is determined by the presence of a nutrient medium, temperature, ability to adapt to life in the water, bactericidal action of sunlight, and the presence in water of bacteriophages and antibiotic substances.
Through the water passed cholera, typhoid fever, paratyphoid a and b, dysentery, leptospirosis, tularemia, polio, epidemic hepatitis, q fever, etc. With contaminated water in the human body can also penetrate the eggs of Ascaris and vlasislav, Giardia cysts, the larvae of the hookworm, cercariae liver Fluke and pathogens other helminthic invasions. Infection can also occur when bathing in the river and through the food ice. When contamination by pathogenic microbes water source, you may experience water epidemics, characterized by the sudden appearance and breadth of coverage of the population (see the Purification of drinking water. Sanitary protection of water bodies).
Hygienic assessment of water. Norms of quality of water supplied to the population permanent centralized drinking water supply, installed on GOST 2874-54 (see water Supply, PL. 3). Hygienic assessment of water local water sources is very responsible and difficult task, as the uniform rules for local water sources due to their diversity cannot be set. The question about the possibility of using water for drinking is decided in each case by the examination and study of the source. The solution to this problem is based on sanitary inspection of the water source and on the comparison of the number of laboratory of chemical and bacteriological analysis of water. In the program of sanitary water analysis usually includes its organoleptic evaluation, the definition of the indicator of water pollution, in particular on pollution with organic substances, and the determination of the water content of some poisonous and harmful substances. The water samples for chemical analysis should be performed in accordance with GOST 4979-49, prepared in accordance with GOST 5215-50.
Bacteriological analysis of water determine microbial the number of bacteria at sowing 1 ml of water, determined by the number of colonies after a 24-hour growing at temperature of 37 degrees) and the title of Escherichia coli (see the Coliform index, e-coli).
According to GOST 2874-54 microbial number of tap water should be no more than 100, e-coli at least 300 ml. Cm. also Sources of water supply.