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Water supply
The total mass of water over, on and under the surface of a planet is called the hydrosphere. The volume of water in Earth’s hydrosphere is 1.4 billion cubic kilometres (320 million cubic miles), but only about 3% of this is fresh water, rather than seawater. A supply of clean, fresh water is vital for drinking, sanitation, farming and industry. Because of climate change, pollution and the overuse of the limited fresh water supply, water shortages are likely to occur in many regions during the 21st century. By tackling overconsumption, recycling waste and reducing pollution, we can conserve our water supply.
What do we use
water for?
Around 70% of the world’s fresh water supply is used in agriculture: water is used to irrigate crops and feed livestock. Industrial uses, accounting for 20%, include hydro-electric power stations, steam turbines, food processing and cleaning. Domestic uses, including drinking, toilet flushing, washing, cooking and garden watering, take up the remaining 10%.
The water industry
In developed, or wealthier, countries, fresh water is supplied directly to homes, farms and factories via a network of pipes. The quality of the supply is strictly regulated. Fresh water is collected in reservoirs and lakes or extracted from springs and wells, which access groundwater contained in water-bearing rock layers called aquifers. It is then purified by filtering, to remove larger particles, and chlorination and boiling to kill harmful bacteria. In some parts of the world, sea water is desalinated (has the salt removed) to make it drinkable. Water that has already been used in homes and factories is then purified in waste water treatment plants and recycled.
Water stress
A country is said to be under “water stress” when the supply falls to less than 1700 cubic metres (60,000 cubic feet) per person per year. At this level, water shortages are experienced at certain times of year. During the 20th century, the world’s population tripled, but its consumption of water multiplied sevenfold. If demand for water continues at its current rate, by the year 2025, around two-thirds of the world’s population will be suffering from water stress.
Water scarcity
around the world
When the supply of fresh water drops to below 1000 cubic metres (35,300 cubic feet) per person per year, an area is said to have “water scarcity”. The southern USA, North Africa, the Middle East and parts of southern Asia and Australia have “physical water scarcity”. This means that, although these regions usually have good water infrastructure, such as pipes, sewers, reservoirs and irrigation canals, they sometimes suffer from a lack of fresh water caused by low precipitation and high demand for water. Around 1.2 billion people live in areas with physical water scarcity.
Parts of Central and South America, sub-Saharan Africa and Southeast Asia suffer from “economic water scarcity”. This means that the water infrastructure of these regions is not developed enough to supply adequate fresh water. Many people have to fetch their water from wells, rivers and lakes—and it may be in particularly short supply during droughts. Around 1.6 billion people live in areas with economic water scarcity. One billion of them have no access to safe drinking water: their water is contaminated with human sewage, disease-causing agents such as bacteria and worms, or chemical waste from factories.
Water crisis
A water crisis is when the demand for unpolluted fresh water in a region constantly exceeds its supply. Symptoms of water crisis include widespread disease caused by drinking polluted water and poor sanitation, low farming yields and conflict over water resources. Countries that have recently experienced water crises include Sudan, Ethiopia and Venezuela. By 2025, 1.9 billion people are likely to live in a region experiencing water crisis. Large-scale migration from these regions is likely to be a major issue in the near future. The arrival of refugees in Europe from Africa's drought-prone Sahel in recent years shows that this migration may have already begun.
Pollution
All over the world, pollution is reducing the supply of fresh water available for drinking, farming and industry. It is also responsible for falling stocks of fish. Even in the USA, for example, around 45% of rivers and streams are too polluted for drinking and fishing. In developing nations, 90% of human sewage goes directly into the water supply untreated, resulting in high levels of pollution.
Consultant: Ian Fairchild
Solutions to water shortage
There are a number of measures that can be adopted, especially in developing nations, to make the best use of existing fresh water supplies. These include:
1. More waste treatment
Investment in sewage disposal systems and increasing the numbers of waste water treatment plants.
2. Improve purification
Introducing low-cost water purification methods, such as solar water disinfection, which uses the sun’s rays to heat water and thus kill disease-causing agents.
3. Use sprinklers
Using sprinklers rather than ditches for irrigation, reducing water usage by up to 90%.
4. Import thirsty crops
For countries with water scarcity, importing certain crops, such as grain, that need a great deal of water to grow, rather than growing them locally.
5. Recycle
Recycling water used in industrial processes rather than expelling it as waste, reducing industrial water use by more than 50%.