Water Quality

Freshwater is a scarce but essential resource, and its quality is of utmost importance as increasing numbers of people and living organisms depend on it for survival. While water scarcity from lack of quantity often receives more attention, water quality becomes more critical than quantity when available water is degraded or polluted. Water quality is important in the ways that it affects human health, livelihoods, agriculture, industry, recreation, and ecosystem services.

Lack of water quality can thus jeopardize socioeconomic development and environmental sustainability, and the availability of clean and good quality water is increasingly recognized as a key factor for sustainable development. Water quality issues are a serious problem in much of the developing world, where lack of access to clean and safe water leads to high rates of morbidity and mortality (e.g., two million children die each year due to inadequate sanitation and clean water). Globally, 1.1 billion people do not have access to safe drinking water, making water quality a serious global concern.

Water can be polluted from a variety of sources, both human-made and natural. Important sources of water pollution can be microbial (viruses, bacteria), chemical (metals, salts, pesticides/herbicides, solid waste), and radiological. Water quality can be measured using a number of parameters: pH, salinity, oxygen content, turbidity, color, odor/taste, dissolved chemicals, total suspended solids, biochemical oxygen demand, and dissolved oxygen. Common water quality treatments include aeration, chemical treatment, filtration, and ultraviolet light treatment. Water quality can be degraded via point source pollution (e.g., oil spills) or diffuse pollution (e.g., agricultural wastewater seepage). Due to the connectivity of groundwater and surface water sources, the pollution of one may threaten the water quality of another connected source. As such, water pollution containment and monitoring is challenged by the flow and connective nature of water, as well as by increasing numbers of sources and types of pollution. How water quality is managed thus reflects society's priorities in water use and management, and the value placed on water quality. Water that is safe for organisms (plants and animals) to survive in, as well as for human use, is at the center of much of the environment-development debates; poor quality water affects different groups of organisms and human society differently across temporal and spatial scales. Given the dialectical nature of human-environment relationships, poor water quality that affects ecosystems also affects society, and vice-versa.

What is deemed to be acceptable levels of pollution of a water source depends on its use, linkages to other water sources, and costs of alternative water usage as well as cleanup or reduction of polluting sources. For instance, agricultural wastewater and industrial effluents can pollute a variety of water sources, making them unsuitable for domestic water purposes as well as aquatic species survival. Pathogens and microbial quality issues are important to humans in drinking water and the spread of waterborne diseases that can affect human society; similarly, overloading of organic matter and chemicals can reduce the ability for aquatic species to survive (e.g., by increasing the biochemical oxygen demand [BOD] to break down pollution). Water quality is generally monitored and regulated through systems of permits and fines that can act as deterrents to pollution or degradation of water sources. Water quality issues become a problem when different uses of a water source are directly threatened. Drinking water quality usually receives the most attention in water quality discussions. When a water source that provides drinking water is contaminated or polluted, it generally becomes important to address that more quickly than nonconsumptive water.

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