Contents
Physical properties, such as density, boiling point, and solubility, are important aspects of Chemistry Topics as they describe the characteristics of substances.
Control Measures of Water Pollution and Conservation of Water
Most of the water which we use comes from the rivers and lakes. Everyday many unwanted and harmful substances are thrown (or discharged) into the rivers and lakes. This makes the water of rivers and lakes impure (or contaminated). And we say that the water has been polluted.
The contamination of water of rivers, lakes and ponds, etc., with unwanted and harmful substances is called water pollution. Water is said to be polluted when it becomes unfit for drinking or bathing. The unwanted and harmful substances which make the water impure (or contaminated) are called water pollutants. In other words, the substances which pollute water are called water pollutants. Pollutants make the water impure.
The major pollutants which cause water pollution are : Sewage, Fertilisers, Pesticides and Industrial wrastes. All these water pollutants are harmful and dangerous to human beings, animals and plants. Some pollutants can even cause death. Hot water from power plants and industries is also considered a pollutant.
This is because when very hot water coming from power plants and industries is discharged into a river or lake, it raises the temperature of the river water (or lake water). This rise in the temperature of river water (or lake water) has an adverse effect on the animals and plants living in it.
Sources of Water Pollution
The water of rivers, lakes and ponds gets polluted by various human activities. The major sources (or causes) of water pollution are given below :
- Dumping of untreated sewage into rivers causes water pollution (see Figure).
- Use of fertilisers in agriculture causes water pollution.
- Use of pesticides in agriculture causes water pollution.
- Discharging of untreated industrial wastes into rivers and lakes causes water pollution.
We will now describe the harmful effects of the water pollutants like untreated sewage, fertilisers, pesticides and untreated industrial wastes, one by one.
1. Untreated Sewage From Homes.
The waste water containing human excreta and carried in sewers (underground pipes) is called sewage. At many places, untreated sewage from homes is dumped into rivers which pollutes the river water. Sewage contains several harmful micro-organisms such as bacteria, protozoa, fungi, viruses and parasites (worms, etc.) which cause serious diseases in humans. The drinking of river water contaminated with sewage can cause water-borne diseases such as cholera, typhoid, diarrhoea, dysentery and jaundice.
2. Fertilisers Used in Agriculture. The farmers use large amounts of chemical fertilisers (like nitrates and phosphates) in the fields to increase the yield of crops. The excess fertilisers dissolve in water and run into rivers, lakes and ponds.
Fertilisers are plant nutrients. So, the fertilisers cause rapid growth of tiny, green, water plants called algae in the river (lake or pond). The algae grow so well by taking fertilisers that they cover the whole surface of water like a green sheet (see Figure).
When the algae complete their life cycle and die, bacteria decompose the huge mass of dead algae by using the dissolved oxygen of water in the river (lake or pond). Due to this the amount of dissolved oxygen in the water of river, lake or pond decreases too much and the fish living in this water die of oxygen starvation. In this way, the water pollution caused by fertilisers used in agriculture decreases the amount of dissolved oxygen in water bodies and leads to the death offish and other aquatic animals.
3. Pesticides Used in Agriculture.
The farmers use toxic chemicals (poisonous chemicals) called pesticides on standing crops in the fields to protect them from pests and diseases. Some of these pesticides dissolve in rain water and run into rivers, lakes and ponds and pollute their water. These poisonous pesticides kill the aquatic animals like fish.
The non-biodegradable pesticides in the polluted water are absorbed by aquatic plants. These aquatic plants are then eaten by aquatic animals like fish. During this, pesticides are transferred from aquatic plants to fish. And when a person eats the fish grown in this polluted water, the pesticides present in fish enter his body and damage his health.
4. Untreated Industrial Wastes.
Almost all the industries produce toxic chemicals (poisonous chemicals) as their waste products. These are called industrial wastes. The untreated industrial wastes are discharged by the industries (or factories) into the nearby rivers or lakes. In this way, the river water or lake water gets polluted with toxic chemicals.
The toxic chemicals present in industrial wastes are the compounds of harmful metals such as mercury, lead, arsenic, nickel and cadmium. These toxic industrial wastes are released by chemical industry, textile industry, leather industry, paper mills, sugar mills, oil refineries, dyes and paint manufacturing industries. The water of rivers and lakes polluted with toxic industrial wastes can kill fish and other aquatic animals which live in this river or lake.
The toxic metal compounds present in this polluted water can enter the human body through the food chain (like eating fish grown in this polluted water). They can damage our nervous system and cause diseases such as blood poisoning and cancer.
Harmful Effects of Water Pollution
The various harmful effects (or ill effects) of water pollution are as follows :
- Drinking of water polluted with untreated sewage can cause diseases such as cholera, typhoid, diarrhoea, dysentery and jaundice.
- Water of rivers and lakes polluted with fertilisers can cause the death of aquatic animals like fish.
- Water of rivers and lakes polluted with pesticides can kill aquatic animals (like fish) and also damage our health (through food chain).
- Water of rivers and lakes polluted with toxic industrial wastes kills the aquatic animals like fish, damages our nervous system and causes diseases such as blood poisoning and cancer.
Pollution of River Ganga
The water of river Ganga has been highly polluted because the villages, towns, and cities which are situated on the banks of this very long river throw large quantities of garbage, untreated sewage, toxic industrial wastes, dead bodies of infants and many other harmful things directly into the river. People immerse idols of gods and goddesses in the river water.
They also throw ashes of dead persons, flowers and polythene bags into the river. People can be seen bathing, and washing dirty clothes and utensils in the river water. They also bathe their cattle like cows and buffaloes in the river. Some people even defecate near the river water. All these uncontrolled human activities pollute the water of river Ganga.
The pollution level in the water of river Ganga has been rising for many years. At present, the pollution level in many stretches of river Ganga is so high that no aquatic animals (like fish, etc.) can survive in it. The river is said to be ‘dead’ at those places (because it cannot support any aquatic life at those places).
A recent study by World Wide Fund for Nature (WWF) has found that Ganga is one of the ten most endangered rivers in the world due to very high level of pollution. An ambitious plan to cleanse the highly polluted river Ganga and save it was launched in 1985. It is called Ganga Action Plan.
The aim of Ganga Action Plan is to reduce the pollution level in the water of river Ganga. However, the increasing population and industrialisation has already damaged this mighty and sacred river beyond repair.
Controlling Water Pollution
The water of most of the rivers and lakes of our country is highly polluted. All of us should make efforts to reduce the pollution of water sources like rivers and lakes. The various ways of controlling (or minimising) water pollution are as follows :
- Sewage should be treated properly at sewage treatment plants to make it harmless before discharging it into nearby rivers.
- Farmers should use correct amounts of fertilisers and pesticides in the fields so that excessive amounts of these harmful agricultural chemicals are not washed into rivers, lakes and ponds.
- All the industries should treat the toxic wastes produced by them suitably to make them harmless before discharging them into rivers.
- Wafer pollution prohibition laws which exist for the industries producing toxic chemical wastes should be implemented strictly by the concerned Authorities.
- Garbage (household waste) should not be thrown into open drains, rivers, lakes or ponds. Dead bodies should not be thrown into rivers. Dead bodies should be cremated or buried properly to prevent pollution of water.
- People should be made aware of the harmful effects of water pollution so that they may co-operate and help in preventing it.
Conservation of Water
The water available in the rivers and lakes is highly polluted and hence not fit for use in homes for drinking or other purposes. The polluted water from rivers and lakes is treated at Water Works and made clean and odourless before supplying it to homes through under-ground pipes.
This treatment of polluted water to make it clean costs a lot of money. We should conserve water by using it carefully, economically and avoiding its wastage (because there is scarcity or shortage of fresh water in our country). The various ways to conserve water (or save water) at home are as follows :
- Turn off the tap immediately after use. Get the leaking taps repaired immediately. A leaking tap that drips even once every second wastes a few thousand litres of water every year.
- Brush your teeth by filling water in a mug. Leaving the tap running while brushing the teeth may waste several litres of water. Take bath by filling water in a bucket and not directly under the running tap.
- Wash the utensils by filling water in a basin and not under the running tap.
- Use water from washing rice, pulses, vegetables and fruits for watering the plants at home.
- Do not use the full flush from the cistern in the toilet when a half flush is sufficient.
Potable Water
The term ‘potable’ means ‘drinkable’. The water which is safe for drinking is called potable water. The tap water which we get through pipes in our home is clean and usually without any foul smell (or odour). It is said to be safe for drinking. Sometimes, however, the tap water which looks clean and has no foul smell may still have some disease-causing micro-organisms (which we cannot see).
Drinking of such water can make a person sick. Thus, clear, transparent and odourless water may not be always safe for drinking (because it may still contain harmful micro-organisms). The tap water can be purified further at home to make it absolutely safe (or fit) for drinking.
The various methods which can be used to make water potable (or safe for drinking) are :
- by filtering (by using porcelain candle filter or electric water filter)
- by boiling, and
- by chlorination (by adding chlorine tablets).
A popular household water filter is a candle-type water filter (which contains one or more candles made of porcelain to filter water). In this type of water filter, the tap water is filled in a container having candles made of porcelain fixed in it. This water gets filtered thoroughly on passing through the tiny pores of porcelain candles and drops into another container kept below. The water which collects in the lower container is very safe for drinking.
In the electric water filter (like Aquaguard) resin filters are used to remove solid particles present in tap water, and ultraviolet radiations are used to kill all the harmful micro-organisms (or germs) present in tap water and make it absolutely safe for drinking. An electric water filter is attached to the tap directly.
Water can be made absolutely safe for drinking by ‘boiling’. When water is heated, it boils at a temperature of 100°C. At this high temperature, all the harmful micro-organisms (or germs) present in water are killed and it becomes absolutely safe for drinking. Many households use boiling as a method for obtaining safe drinking water.
Chlorination is a commonly used chemical method for purifying water. Chlorination is done by adding chlorine tablets to water. Chlorine kills all the harmful micro-organisms (or germs) present in water and makes it absolutely safe for drinking. We should, however, not use more chlorine tablets than specified. Bleaching powder can also be used for chlorination of water and make it safe.
Activity
We can ourselves construct a simple water filter by using the commonly available materials around us. This can be done as follows : Take a plastic bottle and cut it into two halves (keeping the upper part somewhat smaller than the lower part).
Turn the upper half of plastic bottle upside down and place it in the lower half of plastic bottle (so that it may work like a funnel). Make layers in the upper part of water bottle with a piece of fine cloth, followed by cotton, sand and then gravel. Our water filter is ready.
Now pour dirty water from the top end of filter. We will see that clear water collects in the lower half of plastic bottle slowly. The suspended impurities of dirty water have been removed by filtration through the water filter.