Md. Arafat Rahman

Water pollution is the pollution caused by human activities. Polluting substances present in water in natural environment is called water pollution. If inadequately treated wastewater released in natural water bodies, it can cause environmental degradation of aquatic ecosystems. As a result, public health problems may arise among people living downstream. They may drink this contaminated water and use it for bathing or irrigation. Most of the waterborne disease outbreaks that affect or kill people around the world are caused by water pollution.

All plants and organisms that live in or come into contact with contaminated water can be affected. Pollution can destroy individual species and damage the natural ecosystems to which they belong. Many chemicals and pathogens can be cited as causes of water pollution. Contaminants can be organic or inorganic. High temperatures can also cause contamination of water.

A common cause of thermal pollution is the use of water as a coolant in thermal power plants and industrial plants. High water temperature reduce oxygen levels, causing killing fish and changes in the food chain, reducing species ecosystems, and resulting in the emergence of new species of heat-induced bacteria.

Water pollution is measured by analyzing water samples. Physical, chemical and biological tests may be performed. Water pollution can be controlled only by proper infrastructure and management planning. Infrastructure may include wastewater treatment plants. Sewage treatment plants and industrial wastewater treatment plants can protect water bodies from raw wastewater. Agricultural wastewater treatment on farms and erosion control at construction sites can also prevent water pollution.

Another way to prevent water pollution is through nature-focused solutions. Effective control of city sewage systems can be achieved by reducing the flow speed and volume.

In the United States, efforts are being made to reduce water quantity and improve water quality as the best management measures for water pollution. If water is affected by human-borne pollutants, then that water is called polluted. These pollutants can either render the water unfit for human consumption, i.e. undrinkable, or destroy the water's capacity to support organisms, such as fish. Natural phenomena such as volcanoes, algal blooms, storms, earthquakes etc. also cause drastic changes in water quality and its ecological status.

Water pollution is a serious global problem. For this, evaluation and re-evaluation of water policy at all levels is necessary. Water pollution is believed to be the leading cause of disease and death in the world. According to the Global Marine Ecological Survey, water pollution is one of the major environmental problems that could threaten the existence of life on Earth in the coming decades. Water pollution is a major problem for phytoplankton, which produce 70% of the oxygen and absorb a large portion of the Earth's carbon dioxide.

In addition to extreme water pollution in developing countries, developed countries also struggle with pollution problems. Surface water pollution includes pollution of rivers, lakes and seas. One category of surface water pollution is marine pollution. A common route for pollutants to enter the ocean is river water. An example of this is the direct discharge of sewage and factory waste into the sea. This type of pollution is especially common in developing countries.

Plastic waste gets trapped in the ocean. Plastic debris absorbs toxins from marine pollution, which can also enter the body of marine life when they ingest it. These long-lived substances often end up in the stomachs of seabirds and animals. This clogs their digestive tract, leading to decreased appetite or even starvation. Apart from the main pollutants, there are many types of indirect effects. For example, if sediment is floating on the surface of the water, sunlight cannot penetrate through the water and as a result the photosynthesis process of aquatic plants is disrupted.

Specific water pollutants can be of various types, such as chemicals, pathogens, and physical changes such as high temperatures and discoloration. Chemicals and other substances such as calcium, sodium, iron, manganese etc. are known by their concentration in nature, whether they are normal elements of water or contaminants. High concentrations of natural substances can have harmful effects on aquatic plants and animals. Substances that reduce oxygen levels can include natural substances, such as plant parts, or man-made chemicals.

Other natural and anthropogenic substances can cause water turbidity that blocks light penetration, disrupts plant growth, and clogs gills in some fish species. Acidity, electrical conductivity, temperature and eutrophication are factors responsible for changing the physicochemical conditions of water. Eutrophication increases the chemical composition of an ecosystem to increase the primary productivity of the ecosystem. Negative effects on the environment depend on the degree of eutrophication such as anoxia and severe reduction of water quality resulting in loss of fish and other fauna.

Disease-causing microorganisms are called pathogens. These microbes can cause waterborne diseases in humans or animals. Although coliform bacteria are not the actual cause of waterborne disease, they are commonly used as a bacterial criterion for water contamination. Disease-causing organisms are spread to a greater extent from sanitation or inadequately treated sewage at that particular site. Unwanted outfalls in the old infrastructure of old cities can lead to the release of contaminated sewage. Some cities have connected sewage systems that allow polluted water to come out untreated during storms. Poorly managed areas where livestock operations take place can still result in pathogen transmission.

Organic water pollutants include: detergents, disinfection byproducts in chemically sterilized drinking water, such as chloroform, food processing wastes that contain oxygen-demanding substances, fats, greases, pesticides and herbicides, various organohalides, and other chemical compounds, petroleum hydrocarbons, such as fuel and lubricating oils, volatile organic compounds, chlorinated solvents, polychlorinated biphenyls, trichloroethylene, various chemical compounds present in personal hygiene products and cosmetics and drug contamination including pharmaceutical drugs and their metabolites. These molecules are so small that it is difficult to get rid of them without expensive and advanced refineries.

Inorganic water pollutants include: acidity from industrial waste discharges, ammonia from food processing wastes, chemical wastes as by-products of industries, fertilizers containing nitrates and phosphates from agricultural land and also from commercial and domestic uses that are added to rainwater, heavy metals from motor vehicles, and runoff from construction areas. Visible large-scale water pollutants known as floaters in urban storm water runoff – include: human-discarded waste on the ground, small pieces of water-borne plastic and abandoned shipwrecks.

In cities in developed countries, municipal wastewater is specially treated by treatment plants. 90 percent or more of pollutants can be removed by well-designed and managed systems. Some factories have additional measures to remove chemicals and pathogens, but these more advanced treatment steps are becoming increasingly expensive. Eco-based solutions are also being used instead of centralized treatment plants. Low-impact development technologies can also be used to control pollution, such as green roofs and better use of chemicals.

The writer is a, Columnist Southeast University, Dhaka