Water Quality

Why are there variations in water quality?

Water quality differs globally due to various factors, including:

• Agricultural run-off: Factory farming contributes significantly to water pollution, contaminating water sources with fertilizers, pesticides, and animal waste.
• Industrial pollution: Industries often discharge pollutants into rivers and other water bodies, significantly degrading their quality.
• Urban run-off: Urban areas contribute to water pollution through run-off that carries pollutants from cars, factories, and other sources.
• Untreated sewage: Much wastewater is released into the environment without being collected or treated.

Each year, over 80% of the world’s wastewater is discharged untreated into the environment. This pollutes our surroundings and results in the wastage of a renewable resource. While affluent countries have seen improvements in water quality, rivers in many developing regions, particularly in Asia, have become more polluted.

The storage and supply of clean water

Various water supply and management methods are used to store and supply clean water.

Wells and boreholes

These are dug straight down to the water table. Replenished by these wells and boreholes, aquifers provide approximately half of the world’s drinking water, 40% industrial water, and up to 30% irrigation water. For instance, 35% of all public water supply in England and Wales comes from groundwater, which is even more critical in arid and semi-arid regions.

Pipelines

Developed countries generally have more extensive water redistribution networks than developing ones, owing to the high cost of water infrastructure. However, water grids are not as widespread as power grids, limiting the ability to move water from surplus to deficit areas.

Desalination

Desalination is the process of converting seawater into freshwater by removing its salt content. This method is commonly employed in regions such as the Middle East, where other sources of water are scarce. Many desalination plants use distillation, boiling seawater with energy often sourced from waste gases produced by nearby oil wells. Without this waste energy, desalination would be extremely costly. Another method, reverse osmosis, utilises high pressure to filter out salt and is used in places like Singapore and Florida. Although effective, desalination remains expensive, making it less feasible for developing countries unless costs can be significantly reduced.

Cloud Seeding

Cloud seeding is a weather modification technique that enhances rainfall or snowfall by altering cloud formations. It can be employed directly over agricultural land to stimulate rain or used in mountainous areas to increase snowfall. For instance, the technique is widely used in the Rocky Mountains of the USA and Canada to increase winter snowpack, which melts in the spring to provide essential water for downstream areas. Additionally, some ski resorts use cloud seeding to boost snowfall for recreational purposes.

Dams and Reservoirs

In the 20th century, global water consumption increased sixfold, much of it driven by investments in dams and reservoirs. Around 60% of the world’s major river basins are now affected by these structures, and the USA alone has around 80,000 dams of varying sizes. Dams and reservoirs serve multiple purposes, such as regulating water supplies for agriculture, households, and industry, generating hydroelectric power, preventing flooding, and providing transport routes across valleys.

Dams can create “on-channel” reservoirs, where the dam blocks an existing river, or “off-channel” reservoirs, which are natural or man-made depressions near rivers. Some of the world’s largest dams include the Aswan Dam in Egypt, with a reservoir capacity of 132 billion m³, the Tarbela Dam in Pakistan, which stands 143 meters above the Indus River, and the Nurek Dam in Tajikistan, the tallest at 300 meters high.

Since the 1960s and 1970s, dam construction has slowed due to fewer suitable sites, environmental protection concerns, and the increasing cost of materials like concrete. One alternative to building new dams is expanding existing reservoirs. For example, California’s San Vicente Dam was raised by 36 meters at a cost of $530 million, doubling its capacity.

Other water supply and management strategies

Other methods to manage and supply water include:

• Forest Water Management: Managing forests to optimize water supply can improve both the quantity and quality of water available to communities. Protection forests help prevent flooding, soil erosion, and landslides, and they maintain drinking water quality.
• Underground/Mine Storage: Storing water in underground chambers, such as disused mines, reduces evaporation losses and provides a stable water supply.
• Water Licence Exchange: Water pricing and licensing systems allocate specific amounts of water to large users. If license holders do not use their entire allocation, they can sell the surplus under a water licence exchange system.
• Rainwater Harvesting and Grey Water Reuse: Encouraging households to collect rainwater and reuse “grey water” (previously used water, such as from baths) helps reduce reliance on piped water supplies and conserves fresh water for other uses.

Water treatment

Almost all water sources need some degree of treatment to make them safe for human consumption due to contamination from human activities and natural sources.

• Developed countries primarily use central source treatment systems. These involve physical processes like sedimentation, filtration, and disinfectant processes such as chlorination.
• In developing countries, where central treatment systems may be non-existent or lacking capacity, point-of-use (POU) treatment is often employed.
• Compared to surface water, groundwater tends to be relatively cleaner.

Losses in water transport systems are also a significant concern. Well-maintained urban water systems in developed countries lose between 10% and 30% of transported water. In contrast, this loss can be as high as 70% in developing world cities.