i. Point Sources:
These sources discharge water pollutants directly into the water. For example, factories, power plants, underground coal mines, oil wells situated near water bodies, etc. are point sources of water pollution.
ii. Non-Point Sources:
These sources do not have any specific location for discharging pollutants in the water body. For example, run offs from field, lawns, gardens, construction sites, water-logging areas, roads and streets are some non-point sources of water pollution.
Pollution of Freshwater:
Freshwater is naturally occurring water on earth’s surface in ponds, rivers, lakes and streams and groundwater in underground streams. Freshwater has salt concentration of less than 1 % and hence is not saline. Pollution of freshwater is contamination by substances that make it unfit for natural or intended use such as drinking and washing purposes. Freshwater may be polluted by:
i. Domestic sewage discharged into rivers without treating it. Phosphate and nitrate ions from excretory wastes of humans and animals pollute the water. This may cause diseases like typhoid, cholera, dysentery, etc. in the persons drinking such water.
ii. Organic wastes from agricultural fields with phosphate and nitrogen fertilizers that reach lakes, rivers and sea (water becomes deoxygenated and poisonous, thus, cannot support aquatic life).
iii. Industrial wastes (effluents) from urban areas containing high concentration of oil, heavy metals, synthetic detergents and alkalis.
iv. Pesticides, insecticides such as DDT and some industrial waste containing mercury pollute the water and reach the food chain and ultimately in humans, affecting aquatic and human health.
Industrial waste contain harmful chemicals, oils, heavy metals, radioactive waste and suspended solids which when discharged into water, poison it. Since it is difficult to break down waste, they affect the quality of water and pollute it.
Inorganic pollutants like synthetic detergents, acids, salts and toxic metals contain compounds that make the water unfit for use and pollute it. Detergents primarily comprise phosphate, thereby increasing the phosphate levels in water, thus making it unfit for use.
Thermal pollution is the degradation of water quality by any process that changes the temperature of water. Thermal pollution is caused by the water which is used as a coolant by power plants, nuclear power plants and industries.
When this water (after cooling) returns to the natural streams, it is at a very high temperature, making it inappropriate for use. The change in temperature decreases oxygen supply, making it unfit for flora and fauna to survive. It also results in the growth of algae.
Radioactive material enters the water through nuclear power plants, by conducting nuclear tests, spillage from industries and through mining of radioactive elements. When radioactive substances enter the water bodies, especially seawater and oceans, they cause severe damage to the marine ecosystems and even cause gene mutation and other human diseases.
Oil pollution of oceans and rivers is caused due to spillage of oils from oil tankers, accidental spillage, refineries, offshore drilling and cleaning of fuel tanks of ships. On discharge in water, oil spreads on water and forms a layer of oil (oil slick). This is very harmful to aquatic life including fishes, mammals and marine birds.
Marine pollution is the contamination of oceans and seawater. The oceans and seawater mostly get polluted due to sewage, industrial waste, radioactive waste and oil spills.
Effects of Water Pollution:
i. The presence of acids/alkalis in water destroys microorganisms, thereby hindering the self-purification process in rivers.
ii. Water pollution adversely affects the fish and other aquatic life.
iii. The toxic materials may enter the food chain and cause serious health hazards in human beings and other aquatic animals.
iv. Polluted water cause epidemics, such as cholera, tuberculosis, jaundice, dysentery, typhoid and diarrhoea in human beings.
v. The use of polluted water from lakes, ponds and rivers for irrigation of agricultural fields, damages crops and decreases the agricultural production.
vi. Heavily polluted water affects the soil, decreases its fertility and kills soil microorganisms and even certain useful bacteria.
vii. The use of water contaminated with salts increases alkalinity of the soil.
viii. Contamination of seawater due to oil slicks caused by the leakage of crude oil from oil tankers results in the death of sea organisms including fishes.
Prevention and Control of Water Pollution:
Some steps to reduce water pollution are listed below.
i. Setting up sewage water treatment plants before its disposal into rivers
ii. Use of septic tanks in houses to avoid direct outlet of faecal matter and other wastes
iii. Avoid contamination of rivers, lakes and ponds by washing clothes, bathing, etc.
iv. Not throwing waste food materials, paper, biodegradable vegetables and plastic into open drains
v. Effluents from distilleries and solid waste containing organic matter diverted to biogas plants to generate energy.
vi. Treating industrial effluents before discharging into rivers, separate channels for river and sewage water
vii. Total ban on nuclear waste dumping in water
viii. Generating public awareness about the maintenance of ponds, river, lakes and wells in rural and urban areas
ix. Biomedical waste like needles, syringes, soiled dressings, etc. to be disposed properly.