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Water - Factors affecting water supply

Factors affecting water availability

Key words
Over- abstraction - When water is being used more quickly that it is being replaced. This exists where water demand is greater than supply.
Water transfer - Water transfer schemes attempt to make up for water shortages by constructing elaborate systems of canals, pipes, and dredging over long distances to transport water from one river basin to another.

Water is essential to life but water stress threatens supplies.  Water stress occurs when the demand for water exceeds the available amount during a certain period or when poor quality restricts its use. Water stress causes deterioration of fresh water resources in terms of quantity (aquifer over-exploitation, dry rivers, etc.) and quality (eutrophication, organic matter pollution, saline intrusion, etc.). According to the UN:
1. Around 700 million people in 43 countries suffer today from water scarcity.
2. By 2025, 1.8 billion people will be living in countries or regions with absolute water scarcity, and two-thirds of the world's population could be living under water stressed conditions.
3. With the existing climate change scenario, almost half the world's population will be living in areas of high water stress by 2030, including between 75 million and 250 million people in Africa. In addition, water scarcity in some arid and semi-arid places will displace between 24 million and 700 million people.
4. Sub-Saharan Africa has the largest number of water-stressed countries of any region.

Physical factors affecting water availability: climate, geology, rivers
1. Geology – This affects where water is stored and the location of aquifers and groundwater.  Where rocks are impermeable, water remains on the Earth’s surface in rivers.  This is then transferred elsewhere by rivers.  Where rocks are permeable (such as sandstone) then water can infiltrate into the ground and either be moved by underground river systems or be stored.
2. Climate – influences the availability of rainfall, snowfall and rates of evaporation.  Climate can vary over time, with wetter and drier periods, hotter and colder periods.  This can affect water availability. Areas with low rainfall, low groundwater supplies, few lakes or rivers, and generally arid conditions have difficulties accessing water, simply because it is not readily available. An example is Saudi Arabia, where desert conditions mean that there is little accessible fresh water.  Most water must be removed from the ocean and desalinated, a costly procedure.
3. Rivers – river systems move huge quantities of water from where it falls as rain towards seas and lakes.  River systems can dry up in arid zones, so can be unreliable as sources of water.

Human factors affecting water supply:

1. Pollution of water supplies - Freshwater sources around the world are threatened by water pollution. Water resources are under threat through wastage and our thoughtless dirtying  of it. Human activity can pollute both surface and ground water supplies. The main sources of water pollution are the following:
• Discharge of untreated Raw Sewage from households and factories, this can cause cholera, hepatitis and typhoid
• Chemicals and heavy metals (such as lead and cadmium) dumped from Factories
• Agricultural run-offs that make their way into our rivers and streams and groundwater sources.  This can cause eutrophication, where aquatic plants use fertilisers to grow, consume oxygen in lakes and kill other aquatic life.
• Human littering in rivers, oceans, lakes and other bodies of water. Harmful litter includes plastics, aluminium, glass and Styrofoam.

Untreated sewage, Rio Guaíba, Brazil by Paulo RS Menezes [CC BY-SA 3.0 br h], via Wikimedia Commons

Untreated sewage, Rio Guaíba, Brazil by Paulo RS Menezes [CC BY-SA 3.0 br h], via Wikimedia Commons

The cost of technology to clean water makes it impossible for many people in LICs to gain access to clean water.

2. Over abstraction – when too much water is taken out of an aquifer it can limit future water supplies and have drastic consequences.  As Mexico City’s population exploded during the past century, the ability to supply water became insufficient to meet demand.  This resulted in too much groundwater extraction which has contributed to the continued subsidence of Mexico City, which sits below the current level of Lake Texcoco and increases the chance of catastrophic flooding. In the mid-20th century, Mexico City’s ground subsided a reported 40 cm/year in some areas due to the increasing extraction of groundwater. This subsidence can cause pipes to break and sink holes to appear. Over abstraction can also allow salt water to intrude inland, polluting the ground water.

Mexico City Cathedral

Mexico City Cathedral, one of many buildings tilting because of subsidence as a result of over extraction of ground water

3. Water infrastructure and Poverty– this is the pipework, cleaning facilities, waste treatment plants, pumps and storage facilities needed to guarantee water supplies within a country or place.  Many HICs can afford such infrastructure, but people in many poorer countries this isn’t possible.  According to WaterAid, in Nigeria;
• 57 million people in Nigeria don't have access to safe water.
• Over 130 million people don't have access to adequate sanitation in Nigeria, two thirds of the population.
• Almost 60,000 children under five years old die every year from diarrhoeal diseases caused by poor water and sanitation.

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