Water quality describes the chemical, physical, and biological characteristics of water, reflecting its suitability for a particular purpose. It is a fundamental aspect of environmental health, directly impacting aquatic ecosystems and human populations. Maintaining high water quality supports biodiversity, ensures safe drinking water, and facilitates various human activities. Many factors influence water quality, from natural environmental processes to human-induced alterations.
Natural Environmental Influences
The geological makeup of an area influences water chemistry as water moves through the environment. Water flowing through rocks and soils dissolves minerals like calcium, magnesium, and bicarbonates, contributing to water hardness. In regions containing sulfide mineral deposits, natural processes can release heavy metals or increase water acidity.
Weather patterns also significantly shape water quality. Heavy rainfall increases surface runoff, carrying sediments, organic matter, and pollutants from land into water bodies. Water temperature, influenced by air temperature and solar radiation, affects dissolved oxygen levels; cooler water holds more oxygen, essential for aquatic life. Prolonged high temperatures can promote algal growth, impacting oxygen levels and water clarity.
Natural decomposition of organic materials, such as fallen leaves and animal remains, contributes nutrients and organic carbon to water. This process consumes dissolved oxygen as microorganisms break down the material, potentially lowering oxygen levels. Extreme natural events like volcanic eruptions release ash, sulfur, and other chemicals into water systems, altering water chemistry and turbidity. Similarly, large-scale forest fires increase ash, sediment, and nutrient runoff into streams and rivers, affecting water quality for extended periods.
Point Source Contamination
Point source contamination refers to pollutants discharged directly into water bodies from identifiable locations. Industrial facilities release wastewater containing chemicals, heavy metals, and thermal pollution (elevated temperatures) into rivers or lakes. This discharge can impact aquatic life and make water unsuitable for other uses.
Municipal sewage treatment plants can release effluents containing nutrients like phosphates and nitrates, pathogens, and pharmaceuticals if not fully removed during treatment. These substances promote excessive algal growth and introduce harmful microorganisms into receiving waters. Leaking underground storage tanks, often at gas stations or industrial sites, are another point source, releasing petroleum products, solvents, or other chemicals directly into groundwater or adjacent soils. Such leaks can contaminate drinking water supplies and persist.
Mining operations are also point sources, particularly through acid mine drainage. When sulfide minerals in exposed rock contact air and water, they produce acidic runoff containing high concentrations of heavy metals such as iron, aluminum, and copper. This acidic discharge can harm aquatic ecosystems by lowering pH levels and introducing toxic substances, impacting rivers and streams.
Diffuse Contamination Sources
Diffuse contamination, also known as non-point source pollution, originates from widespread areas rather than a single identifiable outlet, often carried into water bodies by rainfall or snowmelt runoff. Agricultural runoff is a major contributor, as excess fertilizers containing nitrates and phosphates wash into streams and rivers, leading to nutrient enrichment and algal blooms. Pesticides and herbicides applied to crops can also be carried by runoff into waterways, posing risks to aquatic organisms and human health. Animal waste from livestock operations introduces pathogens and nutrients into water systems.
Urban stormwater runoff is another diffuse source, picking up pollutants from streets, parking lots, and residential areas during rain events. This runoff can contain oil, grease, heavy metals from vehicle wear, litter, pet waste, and sediment, all of which degrade water quality. Pollutants released into the atmosphere, such as industrial emissions and vehicle exhaust, can travel long distances before settling onto land or directly into water bodies, a process known as atmospheric deposition. This includes acid rain, which lowers the pH of lakes and streams, and mercury, which can accumulate in aquatic food chains.
Failing or improperly maintained septic systems in rural and suburban areas contribute to diffuse contamination by allowing untreated or partially treated wastewater to seep into groundwater or surface waters. This wastewater contains pathogens, nutrients, and household chemicals that can contaminate drinking water wells and degrade nearby rivers and lakes. The cumulative effect of these widespread sources makes diffuse contamination challenging to manage, as it requires addressing practices across large land areas.
Water System Integrity and Treatment
The physical integrity and management practices of water systems influence the quality of water delivered to consumers and returned to the environment. Aging infrastructure, particularly in municipal water distribution systems, can lead to leaks in pipes. These leaks not only result in water loss but also create opportunities for contaminants from surrounding soil or groundwater to enter the drinking water supply, especially during pressure fluctuations. Deteriorated pipes can also contribute to lead or copper contamination if these materials are present.
Inadequate water treatment processes, for both drinking water and wastewater, impact water quality. If drinking water treatment plants lack the capacity or technology to remove specific pollutants, such as industrial chemicals or emerging contaminants like microplastics and pharmaceuticals, these substances can reach consumers. Similarly, outdated or insufficient wastewater treatment facilities may fail to effectively remove nutrients, pathogens, or other harmful substances before discharging effluent into natural waterways, degrading aquatic ecosystems.
Poor waste management practices, including improper disposal of solid waste and hazardous materials, can result in toxic substances leaching into groundwater or entering surface waters during rainfall. Unlined or poorly managed landfills can release leachate containing chemicals and heavy metals, contaminating underlying aquifers. The management of dams and reservoirs also affects water quality by altering natural flow regimes, sediment transport, and water temperature downstream, impacting aquatic habitats and the self-purification capacity of rivers.