Water

Concept: Properties and Purification of Water

As we know, water is an important natural resource, and it possesses some unique properties, which are listed below.

Properties of water:

• Pure water is colourless.
• It does not have a characteristic smell and hence, is odourless.
• It can dissolve many substances, making it an excellent solvent.
• It is liquid at room temperature.
• Water assumes the shape of the liquid in which it is poured.
• It constitutes hydrogen and oxygen in a ratio of 2:1.
• Water is a bad conductor of electricity i.e. it does not allow electricity to pass through it. Still, salts in it make water a good conductor of electricity.
• Example: Tap water (which contains salts) is a good conductor of electricity, whereas distilled water (pure water) is a bad conductor.

States of water:

• Water exists in all three states at different temperatures.
• Water freezes and exists in the solid state at 0°C. The change of water from its liquid state to solid state is called solidification.
• Water boils to form water vapour at 100°C.
• Ice starts melting at the temperature of 4°C.

Soluble and insoluble substances:

• The substances that dissolve in water are called soluble substances.
• Soluble substances can be either solid, liquid or gas.
• The substances that do not dissolve in water are called insoluble substances.
• The method of purification of water depends on the type of impurities present in it.
• Soluble impurities are separated using different methods, while insoluble impurities require other purification techniques.

Methods of purification of water:

1. Evaporation:
• The conversion of the liquid state of water into its gaseous state is called evaporation.
• This method is used to separate soluble impurities like salt or sugar.
• Water containing the soluble impurities is heated.
• Meanwhile, the water evaporates, collected separately, whereas impurities like salt or sugar are left behind as the residue.

2. Sedimentation and Decantation:
• This method is used for removing insoluble impurities like mud and clay particles.
• The water is taken in a container and left undisturbed for a while.
• As a result, the clay and mud particles gradually settle down.
• The clear water from the top is then poured into another vessel, and this method is called decantation.
• Alum, a transparent rock-like substance, is used to increase the rate of sedimentation.
• Dissolving a tiny amount of alum in water increases the weight of the insoluble impurities, which allows them to settle down rapidly.

3. Distillation:
• This method is used to separate water from liquid impurities like oil or alcohol.
• During this process, water is heated up to its boiling point. Water evaporates, leaving behind the impurities.
• The evaporated water vapour is then collected in a condenser, where it condenses to form distilled water.

4. Filtration:
• This method is used to separate insoluble impurities from water by using a strainer, muslin cloth or filter paper.
• The impure water is passed through the above-mentioned things. The impurities accumulate on the strainer, muslin cloth or filter paper while the clear water gets filtered out.
• Impurities like cereals, husk, sand, etc., can be separated by this method.

Water treatment plant

• A water treatment plant is a facility for large scale purification of water.
• The setup consists of various complex machines.
• Water treatment plants are usually built to purify water before it is distributed to the different households in the urban areas.
• These plants also help reduce the impurity levels of industrial wastewater before it is released into nearby waterbodies.
• Water is also recycled in these treatment plants.

Steps involved in the purification of water in a water treatment plant:

1. Primary treatment:
• This step involves filtering and removing large insoluble waste like plastics, wrappers etc.
• The water is then allowed to flow through a screen which does not allow the solid waste to flow ahead.
• Then the separated water is transported to the sedimentation chamber.
2. Secondary Treatment:
• The biodegradable solid waste is allowed to digest by the use of bacteria.
• The bacteria consume the waste matter, which makes the water clearer.
• The water is then left in the sedimentation tank for a while so that the remaining impurities settle down.
3. Disinfection of water:
• The water obtained after the tertiary treatment is treated with chlorine and UV rays is passed through the water which kills the harmful bacteria present.
• This water is then supplied to houses where it is used again and sent back to the water treatment plant through sewage channels.
• In the case of industries, the wastewater, which is released as a result of several chemical processes, is first treated to remove the hazardous chemical substances present in it and then released into the nearby water bodies.
• Such treatment of wastewater is done to reduce the water pollution level.

Judicious use of water:

Implementation of the following habits in daily life would help control the overuse and wastage of water.

We should turn off the tap while brushing our teeth.
Buckets should be used instead of showers for bathing.
Plants should be watered early morning or evening so that the water stays in the soil rather than evaporating quickly.
Water should be reused whenever possible, like the water used for washing vegetables can be used for mopping the floor.
Leaks in the pipes should be repaired immediately to prevent further water wasting.

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