The vast majority of the Earth's water resources are salt water, with only 2.5% being fresh water. Approximately 70% of the fresh water available on the planet is frozen in the icecaps of Antarctica and Greenland leaving the remaining 30% (equal to only 0.7% of total water resources worldwide) available for consumption. From this remaining 0.7%, roughly 87% is allocated to agricultural purposes (IPCC 2007).

According to the Comprehensive Assessment of Water Management in Agriculture, one in three people are already facing water shortages (2007). Around 1.2 billion people, or almost one-fifth of the world's population, live in areas of physical scarcity, while another 1.6 billion people, or almost one quarter of the world's population, live in a developing country that lacks the necessary infrastructure to take water from rivers and aquifers.

One quarter of the global population, or an estimated 1.5 billion people, lacks access to drinkable water.

Health and well-being are intrinsically linked with access to safe, uncontaminated freshwater. An estimated 5 million to 12 million deaths each year are due to illnesses caused by dirty water, according to the National Wildlife Federation.

The world has lost approximately half of its wetlands. This loss reaches far beyond its effect on humans. Freshwater resources are essential habitats for animals and plants. As human demands on freshwater increase, the amount of freshwater available to other species decreases. This demand also threatens the availability of freshwater ecosystem services such as water filtration, fishery maintenance, and the moderation of extremes (for example, floods and droughts). An alarming number of freshwater species — including fish, dolphins, otters, mussels, and amphibians — are already either threatened, endangered, or extinct.

Projections of changes in total annual precipitation indicate that increases are likely in the tropics and at high latitudes, while decreases are likely in the sub-tropics, especially along its poleward edge. Thus, latitudinal variation is likely to affect the distribution of water resources. In general, there has been a decrease in precipitation between 10°S and 30°N since the 1980s (IPCC 2007).

A recent global analysis of variations in the Palmer Drought Severity Index (PDSI) indicated that the area of land characterized as very dry has more than doubled since the 1970s, while the area of land characterized as very wet has slightly declined during the same time period. In certain susceptible regions, increased temperatures have already resulted in diminished water availability. Precipitations in both western Africa and southern Asia have decreased by 7.5% between 1900 and 2005 (Dai et al 2004).

Most of the major deserts in the world including the Namib, Kalahari, Australian, Thar, Arabian, Patagonian and North Saharan are likely to experience decreased amounts of precipitation and runoff with increased warming. In addition, both semi-arid and arid areas are expected to experience a decrease and seasonal shift in flow patterns. If increased temperatures cause an intensification of the water cycle there will be more extreme variations in weather events, as droughts will become prolonged and floods will increase in force (Huntington 2005).

A decline in water quality can result from the increase in runoff and precipitation and while the water will carry higher levels of nutrients, it will also contain more pathogens and pollutants. These contaminants were originally stored in the groundwater reserves but the increase in precipitation will flush them out in the discharged water (IPCC 2007).

Similarly, when drought conditions persist and groundwater reserves are depleted, the residual water that remains is often of inferior quality. This is a result of the leakage of saline or contaminated water from the land surface, the confining layers, or the adjacent water bodies that have highly concentrated quantities of contaminants. This occurs because decreased precipitation and runoff results in a concentration of pollution in the water, which leads to an increased load of microbes in waterways and drinking-water reservoirs (IPCC 2007).

Pesticides and fertilizers used in agriculture and on golf courses and suburban lawns account for a major portion of nonpoint source pollution. Runoff from parking lots and roads flush spilled oil and gasoline and road salt into lakes and streams. Runoff containing manure from livestock and poultry producers has been a major source of surface water pollution. More than 150 pathogens found in livestock manure pose risks to humans. In 2003, concentrated animal feeding operation guidelines, or CAFO standards, were finalized requiring inspection of waste lagoons and outdoor manure tanks, as well as permits for applying manure on land in the US.

Fertilizer, animal manure, and waste-treatment plant effluent all contain nutrients that stimulate excessive plant and algal growth in freshwater bodies. When the plants die and decompose, dissolved oxygen is depleted, causing die-offs of fish and other species living in the water. Persistent organochlorine insecticides, such as DDT, deposited in lake sediments can bioaccumulate, harming the fish and birds that eat them. Pyrethroid insecticides, though derived from chrysanthemums, are extremely toxic to aquatic organisms. Estrogen-mimicking substances such as some pesticides and industrially produced chemicals have been shown to interfere with the reproductive system of fish.

Two-thirds of US estuaries and bays are either moderately or severely degraded from eutrophication (nitrogen and phosphorus pollution).

The Sarno is the most polluted river in Europe, featuring a nasty mix of sewage, untreated agricultural waste, industrial waste, and chemicals.

The King River is Australia's most polluted river, suffering from a severe acidic condition related to mining operations.

Bangladesh has some of the most polluted groundwater in the world. In this case, the contaminant is arsenic, which occurs naturally in the sediments. Around 85% of the total area of the country has contaminated groundwater, with at least 1.2 million Bangladeshis exposed to arsenic poisoning and with millions more at risk.

Each year, plastic waste in water and coastal areas kills up to:
    * 100,000 marine mammals,
    * 1 million sea birds, and
    * countless fish.

Organic Pollution

Organic pollution includes sewage waste, silage effluent, Paper mill waste and dairy wastes. Organic pollution consists of organic (carbon containing) compounds which can be broken down (oxidised) by microorganisms.

As organic pollutants accumulate in water bacterial populations increase because the organic matter contains and provides food for bacteria. Bacteria use up oxygen to break down organic matter. Oxygen levels therefore fall rapidly. The population of fish and clean water invertabrates decreases rapidly because of declining oxygen levels (bacterial activity) and due to the release of toxins from the organic effluent. Species such as sludgeworms (genus Tubificidae) increase in number because organic matter provides plentiful food and a tunnelling medium. Bacterial population decreases as organic matter is used up and protozoa begin to feed on the bacteria. Protozoan population increases accordingly. Sewage fungus population increases and then decreases as organic matter is used up. Larger plants (macrophytes) decline because of the smothering effect of silt or sewage fungus. Algal population decreases initially because of declining light penetration due to sediment and because oxygen concentration declines due to bacterial activity. However, the decomposition of organic matter releases nutrients and allows more light to penetrate, therefore algal population increases.

 Nitrates in Drinking Water

Nitrate concentrations in freshwater have dramatically increased since 1945 because of the increasing use of nitrogenous fertilisers. Nitrates are very soluble and therefore leaching losses can be high. The nitrate may move down through the soil horizons into groundwater reserves, which later become part of the water supply. Large areas of the UK receive drinking water which regularly exceeds the World Health Organisation’s (WHO) 50mg per litre limit.  High nitrate concentrations may lead to the production of nitrosamines in the body, some of which are known carcinogens.

Acidification of Fresh Water

Since carbon dioxide dissolves in atmospheric moisture to form carbonic acid, rain is naturally acidic (pH 5.6). Fossil fuel combustion in power stations and vehicles releases acidic gases which intensify and accelerate the process of acidification.

Acid rain is a misnomer. Acid deposition is a more accurate term since it includes dry deposition, eg. sulphur which falls relatively near to the pollution source, and wet deposition which can be carried thousands of miles before being deposited i.e. it is a trans-boundary pollutant. Acid rain affects fresh water ecosystems both directly and indirectly. Sudden changes in water pH may be lethal to invertebrates and fish. More seriously, when the pH of acidified soils falls below 4.2, aluminium becomes soluble and may enter aquatic ecosystems. High aluminium concentrations:
1. Adversely affect the ability of fish gills to regulate cations such as sodium. The resulting osmotic imbalance can be fatal.
2. Causes excess mucus production which leads to clogging of the gills and suffocation.
3. Interferes with calcification of the skeletons of fish fry and therefore recruitment (the percentage of young fish which develop into adults) decreases and the population decreases. Even gradual acidification will have serious effects on species diversity.

Eutrophication

Eutrophication is the enrichment of fresh water by excess nutrients, usually nitrogen and phosphorus. It is a natural process which humans have greatly accelerated. The nutrient status of lakes increases naturally as sediment constantly reaches it in streams or through direct soil erosion. Thus an oligotrophic (low nutrient, low productivity) lake will inevitably change into a eutrophic one. Accelerated eutrophication has occurred as a result of the following:
1. Increased use of phosphate-containing detergents
2. Increased leaching and run-off from agricultural land
3. Drainage or washings from intensive animal units
4. Bank erosion caused by the swash of boats
5. Increased soil erosion eg. as a result of deforestation

Whereas nitrates are very soluble, phosphates are not and so it usually enters the water as a result of erosion from land. It is, however, a common limiting factor in fresh water and it is usually the extra phosphorus which results in the excess growth of plants so characteristic of eutrophication.
1. With low levels of nutrient input, plant species diversity and abundance may increase. Faunal diversity may also increase because more plants means more food.
2. Microscopic plants (algae) proliferate rapidly causing algal blooms. Although the algae photosynthesise and therefore release some oxygen into the water, by blanketing the surface they severely reduce the amount of light which reaches the lower depths and this reduces the number of larger plants (macrophytes).
3. Zooplankton (microscopic fauna) use macrophytes to escape predation by fish so as macrophyte numbers decrease more zooplankton are eaten so their numbers decrease.
4. As zooplankton numbers decrease, less algae are eaten so algal numbers increase further.
5. Algae have a high turnover rate (productivity and death rate are both high). Dead algae are broken down by aerobic bacteria which use up much of the oxygen in the water.
6. Declining oxygen levels lead to the death of many aerobes (both plants and animals). Many food chains collapse.
7. Dead algae and zooplankton increase the turbidity of the water. Detritus forms sediment.

Thermal Pollution

Tolerance of increasing temperatures varies widely between different species and between different life stages of any one species. However, there are four general effects:
1. Hot effluent kills most bacteria, invertebrates, fish and plants. Some bacteria survive and begin to break down these dead organisms. The rate of metabolic activity increases as temperature increases (effect on enzymes) therefore oxygen is used up faster.
2. Increasing temperature also increases the toxicity of any poisonous substances present in the water.
3. Increasing metabolic activity releases more carbon dioxide which raises the lower oxygen limit which fish can tolerate.
4. As water temperature increases, oxygen solubility decreases therefore oxygen levels drop further.

Toxic Chemicals

The most important categories of toxic chemicals are heavy metals and organic compounds such as polychlorinated biphenyls (PCBs) and pesticides. Although its use in the UK has been banned for many years, the organochlorine pesticide DDT is still widely distributed in the aquatic environment. Such chemicals have been implicated in the serious decline of some top carnivores eg the Otter. Sublethal concentrations reduce reproductive success in fish and fish-eating birds.

PCBs are chlorinated hydrocarbons which have been used in transformers, heat exchangers, lubricating oils, paints and inks. They have entered the aquatic environment from leaking landfills and sewage effluent. As with other organochlorines, PCBs seriously reduce the reproductive ability of mammals.

The lethal effects of toxic chemicals often result from biomagnification - the increasing concentration of a substance up through a food chain. Thus the concentration of toxin found in the tissues of the organisms at the top of the foodchain may be thousands of times greater than the concentration which was released into the environment. Such toxins are often stored in fatty tissue. When this is metabolised to provide energy the toxins are released into the organism's bloodstream, often with fatal effects.

Water is essential to all life and recognised as Sacred to many indigenous and spiritual traditions. Until we again honour the Sacredness of life, and the incredible inter-relationship and inter-dependence of all life forms we will continue to act ignorantly. Thousands of species are already extinct.

Much of the research related to fresh water is dated, and in current documentation, water is largely being related to as a comodity and tool of political leverage. Again, economics factors blinker the essential nature of this life giving element.