• Water pollution occurs when harmful substances—often chemicals or microorganisms—contaminate a stream, river, lake, ocean, aquifer, or other body of water, degrading water quality and rendering it toxic to humans or the environment.

Causes of Water Pollution

• Water is uniquely vulnerable to pollution. Known as a “universal solvent,” water is able to dissolve more substances than any other liquid on earth. It’s also why water is so easily polluted. Toxic substances from farms, towns, and factories readily dissolve into and mix with it, causing water pollution.

Types of Water Pollution

Groundwater 

• When rain falls and seeps deep into the earth, filling the cracks, crevices, and porous spaces of an aquifer (basically an underground storehouse of water), it becomes groundwater—one of our least visible but most important natural resources. 
• Groundwater gets polluted when contaminants—from pesticides and fertilizers to waste leached from landfills and septic systems—make their way into an aquifer, rendering it unsafe for human use.
• Ridding groundwater of contaminants can be difficult to impossible, as well as costly. Once polluted, an aquifer may be unusable for decades, or even thousands of years. Groundwater can also spread contamination far from the original polluting source as it seeps into streams, lakes, and oceans.

Surface water

• Covering about 70 percent of the earth, surface water is what fills our oceans, lakes, rivers etc.
• Nutrient pollution, which includes nitrates and phosphates, is the leading type of contamination in freshwater sources. While plants and animals need these nutrients to grow, they have become a major pollutant due to farm waste and fertilizer runoff. Municipal and industrial waste discharges contribute their fair share of toxins as well. There’s also all the random junk that industry and individuals dump directly into waterways.

Ocean water

• Eighty percent of ocean pollution (also called marine pollution) originates on land—whether along the coast or far inland. Contaminants such as chemicals, nutrients, and heavy metals are carried from farms, factories, and cities by streams and rivers into our bays and estuaries; from there they travel out to sea. Meanwhile, marine debris—particularly plastic—is blown in by the wind or washed in via storm drains and sewers. Seas are also sometimes spoiled by oil spills and leaks—big and small—and are consistently soaking up carbon pollution from the air. The ocean absorbs as much as a quarter of man-made carbon emissions.

Types of Sources

Point source

• When contamination originates from a single source, it’s called point source pollution. Examples include wastewater (also called effluent) discharged legally or illegally by a manufacturer, oil refinery, or wastewater treatment facility, as well as contamination from leaking septic systems, chemical and oil spills, and illegal dumping. While point source pollution originates from a specific place, it can affect miles of waterways and ocean.

Nonpoint source 

• Nonpoint source pollution is contamination derived from diffuse sources. These may include agricultural or stormwater runoff or debris blown into waterways from land. Nonpoint source pollution is the leading cause of water pollution, but it’s difficult to regulate, since there’s no single, identifiable culprit.

Transboundary

• Transboundary pollution is the result of contaminated water from one country spilling into the waters of another. Contamination can result from a disaster—like an oil spill—or the slow, downriver creep of industrial, agricultural, or municipal discharge.

Water Pollutants

• Domestic sewage discharged into rivers from areas located on its banks
• Industrial wastes effluents from urban areas containing high concentration of oil, heavy metals and detergents
• Minerals, organic wastes and crop dusting from agricultural fields with phosphate and nitrogen fertilizers that reach lakes, rivers and sea (water becomes deoxygenated and poisonous, thus, cannot support aquatic life) 
• Chemical fertilizers, pesticides, insecticides, herbicides and plant remains
• Industrial waste water containing several chemical pollutants, such as calcium, magnesium, chlorides, sulphide, carbonates, nitrates, nitrites, heavy metals and radioactive waste from nuclear reactor.
• Excretory wastes of humans and animals in water bodies
• Disposal of urban and industrial waste matter into water bodies

Effects of Water Pollution

• Water pollution adversely affects the fish and other aquatic life. 
• The presence of acids/alkalis in water destroys micro-organisms, thereby disturbing the self purification process in rivers.
• The toxic materials in water cause serious health hazards in human beings and other animals.
• Polluted water causes spread of epidemics, such as cholera, tuberculosis, jaundice, dysentery, typhoid and diarrhoea in human beings.
• The use of polluted water from lakes, ponds and rivers for irrigation of agricultural fields, damages crops severely and decreases agricultural production.
• The use of water contaminated with salts increases alkalinity of the soil.
• Heavily polluted water affects the soil, decreases its fertility and kills soil micro-organisms and even certain useful bacteria.
• Contamination of sea water due to oil slicks caused by the leakage of crude oil from oil tankers causes ecological disasters which results in the death of sea organisms including fishes.
• Fertilizers and pesticides are widely used in agriculture. Their excessive use for increasing agricultural yield has led to the phenomenon of eutrophication and biomagnification.

Some major disturbances in the ecosystem due to water pollution

Eutrophication

With the use of high yielding varieties of crops, the use of fertilizers and pesticides has increased a lot. Excess fertilizers may mix with surface water and may get drained into water bodies (surface runoff). The enrichment of water with nutrients such as nitrates and phosphates that triggers the growth of green algae is called eutrophication. This fast growth of algae followed by decomposition depletes the water body of its dissolved oxygen. As a result aquatic animals die of oxygen shortage.

Sewage and/or fertilizer run off from fields

↓

Enriched nutrient content in lakes (Eutrophication)

↓

Algae multiply to produce an ‘algal bloom’

↓

Algae use up oxygen and begin to die

↓

Decomposers (bacteria) multiply and use more oxygen

↓

Organisms (such as fish) die due to lack of oxygen

Biomagnification

Non-biodegradable pesticides, such as DDT are widely used for crop protection. Once they enter the food chain, their concentration keeps on increasing with each trophic level (steps of a food chain). As a result, accumulation of these compounds takes place in the body of top consumers over a period of time. Entry of harmful non-biodegradable chemicals in small concentrations and their accumulation in greater concentrations in the various levels of food chain is called biomagnification.

Chemical Oxygen Demand (COD) and Biological Oxygen demand (BOD)

• BOD and COD are the two main characteristic properties that indicate the strength of sewage. Both the parameters test the oxygen-demanding strength of the wastewaters.
  • The amount of oxygen that is required for the chemical oxidation of the organic and inorganic chemicals present in the wastewater by utilising oxidising agents like Potassium permanganate, Potassium dichromate etc. is called as chemical oxygen demand (COD). The presence of COD facilitates rapid chemical oxidation of organic matter without any additional equipment. This is the only method that enables to determine the organic load in heavy toxic sewage.
  • BOD is defined as the amount of oxygen demanded by the micro-organisms in the sewage for the decomposition of bio-degradable matter under aerobic condition. This is the most commonly used parameter to determine the strength of municipal or organic quality of the water.

Difference between BOD and COD

Sources of industrial pollution

Prevention and control of water pollution

• Treating industrial effluents before discharging into rivers, separate channels for river and sewage water
• Avoid contamination of rivers, lakes and ponds by washing clothes, bathing. etc.
• Not throwing waste, food materials, paper, biodegradable vegetables and plastic into open drains.
• Setting up sewage water treatment plants
• Use of septic tanks in houses to avoid direct outlet of faecal matter and other wastes
• Effluents from distilleries and solid waste containing organic matter diverted to biogas plants to generate energy

Water pollution in India

• The Sri Lanka-based International Water Management Institute states that India is a water stress zone, where 33% of its
  rivers are moderately or severely polluted.
• Water pollution has infiltrated India’s state of Maharashtra, where a 2021 study conducted by ASAR Social Impact
  Advisors, a Bangalore-based consultancy, and two local research centres, the Center for Sustainable Development
  in Nagpur and Manthan Adhyayan Kendra in Pune, found toxic metals, such as mercury and arsenic, in surface and
  groundwater in 25 locations around fast-growing Nagpur.
• High levels of fluoride, which cause teeth discolouration and potentially other health concerns, have already been
  reported in the groundwater of Amravati-Nagpur and the coastal South Konkan, where 93% of the residents depend on
  it for daily consumption. The researchers stated that their focus is different from others – on the water contamination
  at the power plants and not on the much-studied effects on air, like at Koradi and Khaparkheda.
• The culprit seems to be coal combustion, which is used to produce 70% of the country’s electricity. It creates fly ash,
  which is typically kept in ash ponds that, due to their constructed dikes, sometimes spill into surrounding farms, fields
  and bodies of water. In Nagpur, this water is used by the locals for “drinking (with or without treatment)… domestic use,
  bathing, washing clothes, fishing, irrigation, and water for cattle”, according to the report, ‘Polluted Power: How Koradi
  And Khaperkheda Thermal Power Stations Are Impacting the Environment.

Steps taken by government to combat water pollution

• The Central Pollution Control Board (CPCB) in association with State Pollution Control Boards (SPCBs) / Pollution
  Control Committees(PPCs) is monitoring the quality of water bodies at 2500 locations across the country under
  National Water Quality Monitoring Programme (NWQMP) which indicate that organic pollution is the predominant
  cause of water pollution.
• Based on the magnitude of organic pollution, CPCB in 2008 identified 150 polluted river stretches which increased
  to 302 in 2015. The rivers stretches are polluted mainly due to discharge of untreated / partially treated sewage and
  discharge of industrial wastewater. CPCB assessed the total volume of municipal wastewater generation in the country
  at about 61,948 MLD as against the installed sewage treatment capacity of 23,277 MLD leaving a wide gap of more than
  38,671 MLD. Similar observations were made by WHO in its reports on water pollution.
• The steps taken by the Government to address the issues of water pollution include the following:
  
  • Preparation of action plan for sewage management and restoration of water quality in aquatic resources by State
    Governments;
  • Installation of Online Effluent Monitoring System to check the discharge of effluent directly into the rivers and water
    bodies;
  •  Setting up of monitoring network for assessment of water quality;
  • Action to comply with effluent standards is taken by SPCBs / PCCs to improve the water quality of the rivers;
  • Financial assistance for installation of Common Effluent Treatment Plants for cluster of Small Scale Industrial units;
  • Issuance of directions for implementation of Zero Liquid Discharge;
  • Issuance of directions under Section 5 of Environment (Protection) Act, 1986 to industries and under Section 18(1)
    (b) of Water (Prevention and Control of Pollution) Act, 1974;
  •  Implementation of National Lake Conservation Plan (NLCP) and National Wetland Conservation Programme
    (NWCP) for conservation and management of identified lakes and wetlands in the country which have been merged in
    February, 2013 into an integrated scheme of National Plan for Conservation of Aquatic Eco-systems (NPCA) to undertake
    various conservation activities including interception, diversion and treatment of waste water, pollution abatement, lake
    beautification, biodiversity conservation, education and awareness creation, community participation etc.

Oil Spills

• Oil is an ancient fossil fuel that we use to heat our homes, generate electricity, and power large sectors of our economy.
  But when oil accidentally spills into the ocean, it can cause big problems. Oil spills can harm sea creatures, ruin a day at
  the beach, and make seafood unsafe to eat. It takes sound science to clean up the oil, measure the impacts of pollution,
  and help the ocean recover.

How do oil spills happen?

• There are many types of oil spills and most are minor, for example when oil spills from a ship when it is being refuelled.
  But serious incidents, like the 2020 oil spill in Mauritius, bring consequences that can be felt for decades. Most of the
  major oil spills happen when a pipeline breaks, a tanker sinks or runs aground or when a drilling operation goes wrong.

How do oil spills harm or kill ocean life?

• Where the oil is spilled, what kinds of plants, animals, and habitats are found there, and the amount and type of oil, among
  other things, can influence how much harm an oil spill causes. Generally, oil spills harm ocean life in two ways:
• Fouling or oiling: Fouling or oiling occurs when oil physically harms a plant or animal. Oil can coat a bird’s wings and leave
  it unable to fly or strip away the insulating properties of a sea otter’s fur, putting it at risk of hypothermia. The degree of
  oiling often impacts the animal’s chances of survival.
• Oil toxicity: Oil consists of many different toxic compounds. These toxic compounds can cause severe health problems
  like heart damage, stunted growth, immune system effects, and even death. Our understanding of oil toxicity has expanded
  by studying the effects of the 2010 Deepwater Horizon oil spill.