Water supply Revision Notes

Aquifers are underground layers of permeable rock, sand, or gravel that hold water. They act as natural reservoirs storing fresh water beneath the Earth's surface. People access this water by drilling wells that penetrate the aquifer. Wells can be shallow or deep depending on the depth of the aquifer.

Water from aquifers is generally clean because the soil and rock filter out many impurities. For example, farmers in rural areas often use wells to irrigate crops when surface water is scarce. However, over-extraction can lower the water table, causing wells to dry up or lead to land subsidence. Aquifers recharge slowly through rainfall infiltration, so sustainable use is critical.

• Aquifers store groundwater underground.
• Wells tap into aquifers to extract water.
• Water is usually clean due to natural filtration.
• Overuse can deplete aquifers and cause environmental issues.

Rivers are flowing bodies of surface water that originate from rainfall, melting snow, or springs. They provide fresh water that can be used directly for drinking, agriculture, and industry. For example, many cities draw water from nearby rivers for municipal supply.

River water quantity and quality vary seasonally; during dry periods, flow may reduce, affecting availability. Pollution from upstream activities can also degrade water quality, requiring treatment before use. Managing river water involves balancing ecological needs with human demand.

• Rivers provide accessible surface fresh water.
• Flow varies seasonally affecting supply.
• Water quality can be impacted by pollution.
• Often requires treatment before consumption.

Reservoirs are artificial lakes created by constructing dams across rivers. They store large volumes of water collected during wet periods for use during dry spells. Reservoirs help regulate river flow, provide water for irrigation, hydroelectric power, and domestic use.

For example, the Hoover Dam in the USA creates Lake Mead, supplying water to millions. While reservoirs increase water security, they can disrupt ecosystems, displace communities, and cause sediment build-up behind dams. Proper management is needed to balance benefits and environmental impacts.

• Reservoirs store water by damming rivers.
• Provide regulated water supply year-round.
• Support irrigation, drinking water, and power generation.
• Can have environmental and social impacts.

Desalination plants remove salt and minerals from seawater to produce fresh water, especially in regions lacking natural fresh water sources, such as arid coastal areas. Methods include reverse osmosis and distillation.

For instance, countries in the Middle East rely heavily on desalination to meet urban water demand. Although desalination provides a reliable water source, it is energy-intensive and costly. Environmental concerns include brine disposal, which can harm marine life if not managed properly.

• Desalination converts seawater into fresh water.
• Useful in water-scarce coastal regions.
• Common methods: reverse osmosis, distillation.
• High energy use and environmental considerations.