"WATER"
Water is a chemical compound with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected bycovalent bonds. Water is a liquid at standard ambient temperature and pressure, but it often co-exists on Earth with its solid state, ice, and gaseousstate (water vapor or steam). Water also exists in a liquid crystal state nearhydrophilic surfaces.
Water in three states:liquid, solid(ice), and (invisible)water vapour
in the air. Clouds are accumulations of water droplets, condensed from vapor-saturated air.
Water covers 71% of the Earth's surface, and is vital for all known forms oflife.[4] On Earth, 96.5% of the planet's water is found in oceans, 1.7% in groundwater, 1.7% in glaciers and the ice caps of Antarctica and Greenland, a small fraction in other large water bodies, and 0.001% in the air as vapor,clouds (formed of solid and liquid water particles suspended in air), andprecipitation.[5][6] Only 2.5% of the Earth's water is freshwater, and 98.8% of that water is in ice and groundwater. Less than 0.3% of all freshwater is in rivers, lakes, and the atmosphere, and an even smaller amount of the Earth's freshwater (0.003%) is contained within biological bodies and manufactured products.[5]
Water on Earth moves continually through the hydrological cycle of evaporation and transpiration (evapotranspiration), condensation, precipitation, and runoff, usually reaching the sea. Evaporation and transpiration contribute to the precipitation over land.
Safe drinking water is essential to humans and other lifeforms even though it provides no calories or organic nutrients. Access to safe drinking water has improved over the last decades in almost every part of the world, but approximately one billion people still lack access to safe water and over 2.5 billion lack access to adequate sanitation.[7] There is a clear correlation between access to safe water and GDP per capita.[8] However, some observers have estimated that by 2025 more than half of the world population will be facing water-based vulnerability.[9] A recent report (November 2009) suggests that by 2030, in some developing regions of the world, water demand will exceed supply by 50%.[10] Water plays an important role in the world economy, as it functions as a solvent for a wide variety of chemical substances and facilitates industrial cooling and transportation. Approximately 70% of the fresh water used by humans goes to agriculture.[11]
in the air. Clouds are accumulations of water droplets, condensed from vapor-saturated air.
Water covers 71% of the Earth's surface, and is vital for all known forms oflife.[4] On Earth, 96.5% of the planet's water is found in oceans, 1.7% in groundwater, 1.7% in glaciers and the ice caps of Antarctica and Greenland, a small fraction in other large water bodies, and 0.001% in the air as vapor,clouds (formed of solid and liquid water particles suspended in air), andprecipitation.[5][6] Only 2.5% of the Earth's water is freshwater, and 98.8% of that water is in ice and groundwater. Less than 0.3% of all freshwater is in rivers, lakes, and the atmosphere, and an even smaller amount of the Earth's freshwater (0.003%) is contained within biological bodies and manufactured products.[5]
Water on Earth moves continually through the hydrological cycle of evaporation and transpiration (evapotranspiration), condensation, precipitation, and runoff, usually reaching the sea. Evaporation and transpiration contribute to the precipitation over land.
Safe drinking water is essential to humans and other lifeforms even though it provides no calories or organic nutrients. Access to safe drinking water has improved over the last decades in almost every part of the world, but approximately one billion people still lack access to safe water and over 2.5 billion lack access to adequate sanitation.[7] There is a clear correlation between access to safe water and GDP per capita.[8] However, some observers have estimated that by 2025 more than half of the world population will be facing water-based vulnerability.[9] A recent report (November 2009) suggests that by 2030, in some developing regions of the world, water demand will exceed supply by 50%.[10] Water plays an important role in the world economy, as it functions as a solvent for a wide variety of chemical substances and facilitates industrial cooling and transportation. Approximately 70% of the fresh water used by humans goes to agriculture.[11]
Water pollution
Water pollution is the contamination of water bodies (e.g. lakes, rivers,oceans, aquifers and groundwater). Water pollution occurs when pollutants are discharged directly or indirectly into water bodies without adequate treatmentto remove harmful compounds.
Water pollution affects plants and organisms living in these bodies of water. In almost all cases the effect is damaging not only to individual species and populations, but also to the natural biological communities.
Water pollution is a major global problem which requires ongoing evaluation and revision ofwater resource policy at all levels (international down to individual aquifers and wells). It has been suggested that it is the leading worldwide cause of deaths and diseases,[1][2] and that it accounts for the deaths of more than 14,000 people daily.[2] An estimated 700 millionIndians have no access to a proper toilet, and 1,000 Indian children die of diarrheal sickness every day.[3] Some 90% of China's cities suffer from some degree of water pollution,[4] and nearly 500 million people lack access to safe drinking water.[5] In addition to the acute problems of water pollution in developing countries, developed countries continue to struggle with pollution problems as well. In the most recent national report on water quality in the United States, 45 percent of assessed stream miles, 47 percent of assessed lake acres, and 32 percent of assessed bays and estuarine square miles were classified as polluted.[6]
Water is typically referred to as polluted when it is impaired by anthropogenic contaminants and either does not support a human use, such as drinking water, and/or undergoes a marked shift in its ability to support its constituent biotic communities, such as fish. Natural phenomena such as volcanoes, algae blooms, storms, and earthquakes also cause major changes in water quality and the ecological status of water.
Cause of water
The specific contaminants leading to pollution in water include a wide spectrum of chemicals, pathogens, and physical or sensory changes such as elevated temperature and discoloration. While many of the chemicals and substances that are regulated may be naturally occurring (calcium, sodium, iron, manganese, etc.) the concentration is often the key in determining what is a natural component of water, and what is a contaminant. High concentrations of naturally occurring substances can have negative impacts on aquatic flora and fauna.
Oxygen-depleting substances may be natural materials, such as plant matter (e.g. leaves and grass) as well as man-made chemicals. Other natural and anthropogenic substances may cause turbidity (cloudiness) which blocks light and disrupts plant growth, and clogs the gills of some fish species.[10]
Many of the chemical substances are toxic. Pathogens can produce waterborne diseases in either human or animal hosts.[11]Alteration of water's physical chemistry includes acidity (change in pH), electrical conductivity, temperature, and eutrophication.Eutrophication is an increase in the concentration of chemical nutrients in an ecosystem to an extent that increases in the primary productivity of the ecosystem. Depending on the degree of eutrophication, subsequent negative environmental effects such as anoxia(oxygen depletion) and severe reductions in water quality may occur, affecting fish and other animal populations.
Pathogens
A manhole cover unable to contain asanitary sewer overflow.
Coliform bacteria are a commonly used bacterial indicator of water pollution, although not an actual cause of disease. Other microorganisms sometimes found in surface waters which have caused human health problems include:
- Burkholderia pseudomallei
- Cryptosporidium parvum
- Giardia lamblia
- Salmonella
- Novovirus and other viruses
- Parasitic worms (helminths).[12][13]
Pathogen discharges may also be caused by poorly managed livestock operations.
Chemical and other contaminants
Muddy river polluted by sediment. Photo courtesy of United States Geological Survey.
Contaminants may include organic and inorganic substances.
Organic water pollutants include:
- Detergents
- Disinfection by-products found in chemically disinfected drinking water, such aschloroform
- Food processing waste, which can include oxygen-demanding substances, fats and grease
- Insecticides and herbicides, a huge range of organohalides and other chemical compounds
- Petroleum hydrocarbons, including fuels (gasoline, diesel fuel, jet fuels, and fuel oil) and lubricants (motor oil), and fuel combustion byproducts, from stormwater runoff[16]
- Tree and bush debris from logging operations
- Volatile organic compounds (VOCs), such as industrial solvents, from improper storage.
- Chlorinated solvents, which are dense non-aqueous phase liquids (DNAPLs), may fall to the bottom of reservoirs, since they don't mix well with water and are denser.
- Perchlorate
- Various chemical compounds found in personal hygiene and cosmetic products.
A garbage collection boom in an urban-area stream in Auckland, New Zealand.
Inorganic water pollutants include:
- Acidity caused by industrial discharges (especially sulfur dioxide from power plants)
- Ammonia from food processing waste
- Chemical waste as industrial by-products
- Fertilizers containing nutrients--nitrates and phosphates—which are found in stormwater runoff from agriculture, as well as commercial and residential use[16]
- Heavy metals from motor vehicles (via urban stormwater runoff)[16][17] and acid mine drainage
- Silt (sediment) in runoff from construction sites, logging, slash and burn practices or land clearing sites.
Macroscopic Pollution
Macroscopic pollution—large visible items polluting the water
Trash or garbage (e.g. paper, plastic, or food waste) discarded by people on the ground, along with accidental or intentional dumping of rubbish, that are washed by rainfall intostorm drains and eventually discharged into surface waters
- Nurdles, small ubiquitous waterborne plastic pellets
- Shipwrecks, large derelict ships.
Thermal pollution is the rise or fall in the temperature of a natural body of water caused by human influence. Thermal pollution, unlike chemical pollution, results in a change in the physical properties of water. A common cause of thermal pollution is the use of water as acoolant by power plants and industrial manufacturers. Elevated water temperatures decreases oxygen levels (which can kill fish) and affects ecosystem composition, such as invasion by new thermophilic species. Urban runoff may also elevate temperature in surface water.