Tastes and smells, characteristic for water of natural sources, occur frequently owing to natural or artificial pollution. Four basic tastes of water are distinguished: salty, bitter, sweet and sour. All other numerous shades of flavouring sensations develop from basic and are named smacks. The most widespread salty taste of water is in most cases is caused by NaCl dissolved in it, bitter - by MgSO4; sour taste have the mineral waters containing surplus of dissolved carbonic acid; the ink and ferruterous smack to water is given by the salt of iron and manganese, dissolved in it, alkaline - by soda. The threshold of flavouring perception of salt additives to water is characterised by the following concentration (mg/l): NЮяl - 165; яЮяl₂ - 470, лgяl₂ - 135; лnCl₂ - 1,8; FeCl₂ - 0,35;
лgSO₄ - 250; яЮSO₄ - 70; лnSO₄ - 15,7; FeSO₄ - 1,6; NaHCO₃ - 450. On force of influence on bodies of taste the ions of metals are divided into following lines: NH₄⁺ > NЮ⁺ > й⁺; FЕ²⁺ > лn²⁺ > лg²⁺ > яЮ²⁺; anions - into a line: нм^- > NO₃^- > яl^- > мян₃^- > SO₄^2-. Deterioration of flavouring qualities of water can be caused by organic substances, present in water. However taste in this case is more often masked by dominant smell. The smells of water are usually divided into two groups: smells of a natural origin caused by products of lifes and disintegration of various organisms, and smells of an artificial origin arising in the result of descent of industrial waste water in a reservoir. The characteristic of smells is given descriptively: fish, chemist's, smell of petroleum, fenolian, chloric etc. Cane gives water the smell of marsh, fish, spread out greens, wet straw etc. The most significant deterioration of smell and taste parameters of water is observed during mass development of seaweeds in it. During the development of bacteria in water it gets aromatic (pleasant and unpleasant), sour smells, and also smells similar to a smell of petrol, spirit, ammonia etc. During the pollution of water by industrial drains in most cases appreciable deterioration of flavouring qualities and smells of water occurs at the rather insignificant contents of organic impurity in it. Sometimes these quantities are less than the concentration of very difficultly soluble substances (1 part on more than 1 000 000 parts of water). For example, chlorfenol is found out on taste at the concentration of 0,000004 mg/l, that approximately corresponds to its one molecule on 10¹² not having smells and taste of molecules of water.