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Дата: 29.01.2018

вода (2006)

Water distribution in subsurface drip irrigation Irrigation of field crops The most important use of water in agriculture is for irrigation , which is a key component to produce enough food. At the time, there were fewer than half the current number of people on the planet.

People were not as wealthy as today, consumed fewer calories and ate less meat, so less water was needed to produce their food. They required a third of the volume of water we presently take from rivers. Today, the competition for the fixed amount of water resources is much more intense, giving rise to the concept of peak water.

To avoid a global water crisis, farmers will have to strive to increase productivity to meet growing demands for food, while industry and cities find ways to use water more efficiently. While cotton accounts for 2. Significant environmental damage has been caused, such as disappearance of the Aral Sea.

Work was therefore commissioned to determine precisely the mass of one liter of water. Natural water consists mainly of the isotopes hydrogen-1 and oxygen-16, but there is also a small quantity of heavier isotopes such as hydrogen-2 deuterium. The amount of deuterium oxides or heavy water is very small, but it still affects the properties of water.

Water from rivers and lakes tends to contain less deuterium than seawater. For drinking A young girl drinking bottled water Water availability: Most of this is ingested through foods or beverages other than drinking straight water.

It is not clear how much water intake is needed by healthy people, though most specialists agree that approximately 2 liters 6 to 7 glasses of water daily is the minimum to maintain proper hydration. People can drink far more water than necessary while exercising, however, putting them at risk of water intoxication hyperhydration , which can be fatal.

Most of this quantity is contained in prepared foods. The Institute of Medicine U. Water is excreted from the body in multiple forms; through urine and feces , through sweating , and by exhalation of water vapor in the breath.

With physical exertion and heat exposure, water loss will increase and daily fluid needs may increase as well. Humans require water with few impurities. Some solutes are acceptable and even desirable for taste enhancement and to provide needed electrolytes. Washing is also an important component of several aspects of personal body hygiene. Most of personal water use is due to showering , doing the laundry and dishwashing , reaching hundreds of liters per day in developed countries.

Ship transport The use of water for transportation of materials through rivers and canals as well as the international shipping lanes is an important part of the world economy. Chemical uses Water is widely used in chemical reactions as a solvent or reactant and less commonly as a solute or catalyst. In inorganic reactions, water is a common solvent, dissolving many ionic compounds, as well as other polar compounds such as ammonia and compounds closely related to water.

In organic reactions, it is not usually used as a reaction solvent, because it does not dissolve the reactants well and is amphoteric acidic and basic and nucleophilic. Nevertheless, these properties are sometimes desirable. Also, acceleration of Diels-Alder reactions by water has been observed. Supercritical water has recently been a topic of research. Oxygen-saturated supercritical water combusts organic pollutants efficiently. Water vapor is used for some processes in the chemical industry.

An example is the production of acrylic acid from acrolein, propylene and propane [66] [67] [68] [69]. The possible effect of water in these reactions includes the physical-, chemical interaction of water with the catalyst and the chemical reaction of water with the reaction intermediates.

Heat exchange Water and steam are a common fluid used for heat exchange , due to its availability and high heat capacity , both for cooling and heating. Cool water may even be naturally available from a lake or the sea. A disadvantage is that metals commonly found in industries such as steel and copper are oxidized faster by untreated water and steam. In almost all thermal power stations , water is used as the working fluid used in a closed loop between boiler, steam turbine and condenser , and the coolant used to exchange the waste heat to a water body or carry it away by evaporation in a cooling tower.

In the United States, cooling power plants is the largest use of water. In most nuclear reactors , water is both a coolant and a moderator. This provides something of a passive safety measure, as removing the water from the reactor also slows the nuclear reaction down.

However other methods are favored for stopping a reaction and it is preferred to keep the nuclear core covered with water so as to ensure adequate cooling. Fire extinction Water is used for fighting wildfires. Water has a high heat of vaporization and is relatively inert, which makes it a good fire extinguishing fluid. The evaporation of water carries heat away from the fire. It is dangerous to use water on fires involving oils and organic solvents, because many organic materials float on water and the water tends to spread the burning liquid.

Use of water in fire fighting should also take into account the hazards of a steam explosion , which may occur when water is used on very hot fires in confined spaces, and of a hydrogen explosion, when substances which react with water, such as certain metals or hot carbon such as coal, charcoal , or coke graphite, decompose the water, producing water gas.

A steam explosion occurred when the extreme overheating of the core caused water to flash into steam. A hydrogen explosion may have occurred as a result of reaction between steam and hot zirconium. Recreation Grand Anse Beach, St. Some of these include swimming, waterskiing , boating , surfing and diving.

In addition, some sports, like ice hockey and ice skating , are played on ice. Lakesides, beaches and water parks are popular places for people to go to relax and enjoy recreation. Many find the sound and appearance of flowing water to be calming, and fountains and other water features are popular decorations.

Some keep fish and other life in aquariums or ponds for show, fun, and companionship. Humans also use water for snow sports i.