Package of information about natural water you do not know so far.

 Sources of water

People in the village may be getting water from a well or a river whereas in a city we get water in our homes through taps where water is supplied by the municipality.

Each of us may be getting water into our homes in different ways. But finally, all of us get the water from some big source; a river, well or a lake.

Water as it occurs in nature is called natural water. The various forms of natural water are rainwater; river water, water from ponds, lakes, streams and underground water (water from the well)

Rainwater

It is the purest form of water available in nature. The first showers of rain collect dust; bacteria, and germs and dissolve some of the gases present in the atmosphere. Subsequent showers are free from such impurities.

River water

Water which flows on the surface of the earth making a regular course is the river water. It is very impure as it contains both suspended and dissolved impurities.

It may also contain sewage, chemical and toxic waste flowing into it from a nearby town, village or industry (The Ganges river flowing near Kanpur city is polluted because of the chemical wastes being flown into the river from various shoe factories of Kanpur).

Sea water

Rivers ultimately flow into the sea. So, all the impurities are carried into the sea. Sea water is very salty and impure from natural water. Yet the oceans play an important role in supplying the water we get through the water cycle.

Spring or well water (groundwater)

Rainwater falls into rivers and seas. Some of it evaporates and mixes in the air. The rest is absorbed by the ground and is called groundwater. The surface of the groundwater is called the water table.

 The level of the water table is not fixed and varies from place to place depending on the condition of the soil and the amount of rainfall. This water reappears at several places in the form of spring water.

Sometimes this water is obtained by digging wells and well water. Spring or well water is purer than sea river water but less pure than rainwater. It still contains some impurities from the earth‘s crust and needs to be purified before drinking.

Potable water

The water fit for human consumption is called potable water. It should have the following properties.

Clear, odourless and colourless.

Free from harmful bacteria and suspended impurities.

Contains dissolved gases like oxygen and carbon dioxide as they impart freshness and a sparkling appearance.

Water contains small amounts of mineral salts like sodium, calcium and magnesium are required by body metabolism. However excess of these minerals can be harmful.

Potable water may be prepared from ordinary water by Boiling, Chemical treatment, and Distillation.

Electrolysis of water

Classifications

The process of breaking down a compound by passing an electric current through it is called electrolysis. The electrolysis of water produces hydrogen and oxygen in the ratio of 2:1 by volume.

Physical properties of water

Water is a neutral oxide and has no effect on litmus paper. It is a colourless, transparent liquid at room temperature. Pure water is tasteless and odorless.

Pure water boils at 100^oC and freezes at 0^oC at sea level, where the atmospheric pressure is the greatest. The boiling point of water decreases if the pressure is lowered and increases if the pressure is raised. The melting point of ice is lowered if the pressure is increased.

Chemical properties of water

Many metals react with water to produce oxides and hydroxides.

Sodium and potassium react with cold water vigorously.

2Na + 2H₂O → 2NaOH + H₂

Magnesium reacts slowly with cold water.

Mg + 2H₂O → Mg (OH) ₂ + H₂

Zinc reacts with, while iron reacts with steam.

Reaction with oxides – water reacts with metallic oxides to form bases.

Na₂O + H₂O → 2NaOH

Hard water

Hard water has a high mineral content consisting of bicarbonates, sulphates of calcium and magnesium. Hard water is generally not harmful. The simplest way to determine the hardness of water is the lather (or) froth test with soap or toothpaste, when agitated, lathers easily in soft water but not in hard water.

Hard water is not fit for

Drinking as it upsets the stomach.

Washing clothes or bathing forms sticky and wastes soap.

Forms scales on the walls of boilers.

Dyeing as the colours tend to fade.

Soft water

Contains few or igneous rock sources, such as granite but may also derive from sandstone sources, since such sedimentary rocks are usually low in calcium and magnesium.

There are water softening devices that are used in houses, and industries to remove the minerals causing hardness. Artificially softened water is beneficial as scales are not formed in the pipes, boiler or hot water cylinder which is due to the deposition of calcium carbonates.

Temporary hardness

The temporary harness is caused by a combination of calcium ions and bicarbonate ions in the water. Harness in water is caused by the presence of calcium ions, magnesium ions, or both.

As their concentrations increase, water becomes harder. The combined concentration of calcium and magnesium is frequently referred to as total hardness. Hard water containing bicarbonate of calcium and magnesium can be removed from boiling water.

The good thing about temporary hardness is that it is easy to remove by boiling or through precipitation with lime (calcium hydroxide). Boiling and adding lime are two of the older methods used to soften water containing temporary hardness.

Permanent hardness

Permanent hardness is hardness (mineral content) that cannot be removed by boiling. It is usually caused by the presence of calcium and magnesium sulphates and/or chlorides in the water, which become more soluble as the temperature rises. They can be removed by several methods. One method is treating with washing soda.

CaCl₂ + NaCO₃ → 2Nacl + CaCO₃

MgCl₂ + Na₂CO₃ → 2Nacl + MgCO₃

CaSO₄ + Na₂CO₃ → Na₂SO₄ + CaCO₃

MgSO₄ + Na₂CO₃ → Na₂SO₄ + MgCO₃

Solubility of solids

Water is called a universal solvent because a large number of substances dissolve in it. Water is an excellent solvent. The solubility of a solute is the amount of it that dissolves in a unit amount of water and the solubility of a solid increases with the temperature.

When a solution contains as much solute as it can hold, it is called saturated. The solubility of a gas increases with the increase in pressure and decreases with the increase in temperature.

Water exists in three states – solid, liquid and gas. The continuous cycling of water among its three forms keeps the total amount of water constant. This is known as the water cycle.

The water table goes down if the usage is more than the replenished water through rain and seepage. Water harvesting is one of the methods of recharging groundwater.

It is done by constructing pits to which rainwater is diverted and deposited. This increases the groundwater level. Sewage is liquid waste. The impurities in water are called contaminants. Chemicals used in agriculture, factories and human waste contaminate water.

Wastewater treatment plants (WWTP) clean water before its disposal by using a series of processes like filtration, sedimentation, skimming, treatment with anaerobic and aerobic bacteria chlorination, etc. We all must ensure the economy in the use of water and make all our efforts for the conservation of water.