Municipal wastes, human and animal wastes, and industrial effluents are major sources of water pollution. Untreated sewage, human and animal excreta, and industrial wastewater contain pathogens, nutrients, and toxic metals that make water unsafe for drinking and aquatic life. Common pollutants include oxygen-demanding wastes, nutrients like nitrogen and phosphorus that cause algal blooms, suspended solids, salts, and toxic compounds. These pollutants contaminate surface and groundwater sources and disrupt ecosystems.

1. Causes of Water Pollution
The Industrial development Urbanization and for achieving more comforts in life, the human has polluted the
surrounding including the aquatic environment. Most of the available water either surface or underground is severely
polluted. A number of factors causing to contaminate potable water are;
• Municipal Wastes: It comprise of the human excreta, sewage, kitchen wastes and storm water allowed to flow into
drains, sewers, canals, and rivers in untreated state, causing to pollute water bodies. The sewage is also used for
irrigation without undergoing proper treatment. The wastewater has certain amount of nitrates, phosphates and
potassium (NPK), which provide the essential nutrients for the growth crops.
• Human and animal wastes contains pathogenic microorganisms like bacteria, viruses, protozoa and worms. These
harmful organisms caused to make the surface and subsurface resources polluted. The human beings and other
animals are affected when they come in contact or consume the contaminated aquatic life. Wastewater is produced at
a rate of 70-80% of the consumed quality. This contains biological, inorganic, organic and industrial compounds,
therefore more BOD is required for its treatment.
•Industrial Effluents: Industrial effluents consists of organic and inorganic salts, pathogenic organisms, toxic
materials, metal scraps, acids, alkalis, heavy metals etc. Pakistan is facing the serious dilemma of industrial pollution.
The wastes and effluents are being dumped in water courses untreated. At least 50 metals have been detected in the
effluents and these includes Mercury, Cadmium, Chromium and lead which are extremely harmful for human health.

2. Water Pollutants
Clean water has to be used for intended purpose, and then returned will be polluted. The agents caused to pollute
water is pollutant. The major pollutants are (i) Oxygen Demanding wastes (ii) Nutrients (iii) Pathogenic organisms
(iv) Suspended solids (v) Salts and other dissolved solids (vi) Toxic metals and Organic compounds (vii) Heat
Oxygen Demanding wastes (ODW): Oxygen demanding wastes are substances that oxidize in water. As
microorganisms decompose these wastes, they utilize oxygen dissolved in water, which reduce the concentration of
DO. As DO drops, fish and other aquatic life are threatened and in extreme case, killed. The critical level of DO
varies greatly among species. Like trout and salmon species of fish required cold water with DO of 7.5 mg/l, while
carp can survive at 3 mg/l. The US-EPA recommended 4 mg/l of DO for various species of fish survival. The low
level of DO produced undesirable odor, tastes and color reduce the attractiveness for domestic and for recreational
purposes. ODW are biodegradable organic and inorganic substances present in municipal wastewater or in effluents
from various industries like food processing and paper production. Similarly the natural organic matters like plant
leaves and dead animals if disposed up in water contribute to oxygen depletion. There are several measures of DO
like COD and BOD.
Nutrients: Nutrients are chemicals like nitrogen, phosphorus, carbon, sulfur, calcium, potassium, iron manganese,
cobalt and boron that are essential to the growth of plants. In case of water quality, nutrients are pollutants when
high concentration caused growth of algae. The presence of algae adversely affect the quality of water for drinking
and recreational purposes. The decomposition of algae used DO from water leaving less concentration for other
aquatic life. Algae and decaying materials add color, turbidity, and objectionable taste to water, that are difficult to

3. Water Pollutants
to remove. Aquatic species require a number of nutrients for their growth and reproduction. The three important
nutrients are carbon, nitrogen and phosphorus. Plants require large amounts of these three nutrients and the deficiency
caused to limit the growth. The nutrients that is less available than the demand is known as limiting nutrients. The
algal
growth can be controlled by reducing the supply of these nutrients. The Carbon is usually available from various
sources like alkalinity, dissolved CO2 from atmosphere and decaying organic matter, so it is not a limiting nutrient.
The major sources of Nitrogen are municipal wastewater, runoff from animal feedlots, chemical fertilizers and
nitrogen
deposition from atmosphere, certain bacteria and blue-green algae. It is very difficult to control nitrogen specially in
lakes. Nitrogen presence in drinking water is usually in the form of Nitrate (NO3), which it self is not toxic. However
certain bacteria found in the infant intestinal convert Nitrate to high toxic Nitrite (NO2) . Hemoglobin in the blood
stream has more affinity for nitrite than oxygen and when oxygen is replaced by nitrites it is known as
methemoglobinemia. It causes a bluish discoloration of the infant, and is commonly known as blue baby syndrome.
Phosphorus is another essential nutrient for plant growth. Human sources of phosphorus are the agricultural runoff
of heavy fertilizers and domestic sewage. In sewage phosphorus is from human feces and part of Detergents.
Phosphorus in detergents is usually in the form of sodium tripolyphosphate Na2 P3 O10. when wash water
containing this ingredient is discarded the following reaction occurs and slowly releases the orthophosphate

4. Water Pollutants
• Pathogenic organisms: Pathogens are disease causing microorganisms that grow and multiply within the host.
The growth of microbes in a host is infection. Pathogens may be bacteria, viruses and protozoa responsible for
several diseases like cholera, dysentery, typhoid, hepatitis, malaria etc. The intestinal discharges of an infected
individual, a carrier may contain billions of pathogens, which if allowed to enter in water supply can cause
epidemic diseases. The carrier may not necessary to have symptoms of diseases, which makes it even more
difficult to protect water supply from contaminations. If concentration of pathogens are high, such water may
also not fit for swimming and fishing purposes. Certain shellfish can be toxic because they concentrate
pathogenic organisms in their tissue, making the toxicity levels in the shellfish much greater than the levels in
the surrounding water.
• Suspended Solids: Organic and inorganic particles that are carried by the wastewater into a receiving water is
termed suspended solids. When the speed of water is reduced by flowing into a lake or reservoir, many of these
particles settles to the bottom as sediments. Similarly when eroded soil particles are being carried by water and
are not settled are sediments. Colloidal particles when do not settle easily caused turbidity. Organic suspended
solids may also exert DO. When sediments are deposited in lakes and reservoirs their usefulness is reduced. In
some rapidly moving mountain streams, sediment from mining and logging operations has destroyed many living
places for aquatic organisms.
• Salts and other Dissolved solids: Water naturally accumulates a variety of dissolved solids and salts as it passes
through soils and rocks on its way to sea. The salts includes cations such as Sodium, Calcium, Magnesium, and
potassium while the common anions are Chloride, Sulfate and bicarbonate.

5. Water Pollutants
The presence of these dissolved cations and anions are termed as total dissolved solids (TDS). Fresh water usually
have less than 1500 mg/l TDS. Brackish water have up to 5000 mg/l, saline water above 5000 mg/l and sea water
more than 30,000 mg/l. The concentration of TDS is an indicator of the usefulness of water for various applications.
Like drinking water upper limit is 500 mg/l, livestock upto 10,000 mg/l. For crop production more than 500mg/l is a
problem for salt tolerance crops, while more than 2100 mg/l need proper drainage system. All naturally occurring
water has some amount of salt in it. A number of industries discharge high concentration of salts and urban runoff
may contain large amounts where salts is used to keep ice from forming on roads in winter season.
Similarly, the evapotranspiration increases salinity problem. The concentration in soils is usually controlled by
flushing the salts with additional amount of irrigation water. This process increase the cost as well as contaminate
water. If proper drainage is not available, then water table raises up along with dissolved salt and damage crops.
Toxic Metal and Organic Compounds: Most metals are toxic, like aluminum, arsenic, cadmium, chromium,
mercury
Lead, iron and zinc. Some of these metals like chromium and iron are essential nutrients in out diet, but in high
doses they can cause a range of adverse impacts on the body, including nerves system and kidney damage
etc. Metals are non degradable and creates problems for human beings if their concentration increases in body.
The chemicals that can be used for killing of organisms are insecticides, herbicides, rodenticides and
fungicides..The three main group of synthetic organic insecticides are organochlorines also known as chlorinated

6. Water Pollutants
hydrocarbons, organophosphates and carbamate. The most widely used organochlorine is DDT
(dichlorodiphenyl trichloethane) is widely used to control insects, but are very persistent and soluble. It is
very toxic to human beings and caused a number of diseases including cancer. Agricultural runoff often
contains such agro-chemicals that has been applied on crops. Industrial wastewater contains either toxic
metals or organic compounds if discharged in large quantities, make water unfit for intended purposes. Many
toxic Compounds are concentrated in food chain, making fish unsafe for human consumption. Thus even
small quantity of toxic compounds in water can be incompatible with the natural ecosystem and human use.
Heat: The thermal and nuclear electric power plants requires large amount of cooling water. For example
nuclear power plant warms about 150,000 m3/hr of cooling water by 10C0 as it passes through the plant
condenser. If that heat is released to a local river or lake, the resulting rise in temperature can adversely
affect life in the vicinity of thermal plume. For some fish like trout any increase in temperature is life
threatening, while for other warm water is beneficial upto certain extent. Also the sudden change in
temperature caused by plant can disturb the local ecology. Similarly the water releases by different industries
are much hotter than the receiving waters. In some case hot water increases the metabolic activities of fish,
causing more population. The demand of dissolved oxygen increases with the same rate, but the
concentration reduces due to more consumption as well as the absorb capacity for DO is less in hot water
than cool water. Similarly high temperatures increase the rate of oxygen depletion when oxygen demanding
wastes are presents.

7. Water Pollutants
hydrocarbons, organophosphates and carbamate. The most widely used organochlorine is DDT
(dichlorodiphenyl trichloethane) is widely used to control insects, but are very persistent and soluble. It is
very toxic to human beings and caused a number of diseases including cancer. Agricultural runoff often
contains such agro-chemicals that has been applied on crops. Industrial wastewater contains either toxic
metals or organic compounds if discharged in large quantities, make water unfit for intended purposes. Many
toxic Compounds are concentrated in food chain, making fish unsafe for human consumption. Thus even
small quantity of toxic compounds in water can be incompatible with the natural ecosystem and human use.
Heat: The thermal and nuclear electric power plants requires large amount of cooling water. For example
nuclear power plant warms about 150,000 m3/hr of cooling water by 10C0 as it passes through the plant
condenser. If that heat is released to a local river or lake, the resulting rise in temperature can adversely
affect life in the vicinity of thermal plume. For some fish like trout any increase in temperature is life
threatening, while for other warm water is beneficial upto certain extent. Also the sudden change in
temperature caused by plant can disturb the local ecology. Similarly the water releases by different industries
are much hotter than the receiving waters. In some case hot water increases the metabolic activities of fish,
causing more population. The demand of dissolved oxygen increases with the same rate, but the
concentration reduces due to more consumption as well as the absorb capacity for DO is less in hot water
than cool water. Similarly high temperatures increase the rate of oxygen depletion when oxygen demanding
wastes are presents.