Natural Water Resources

• Water is one of the most important commodities for survival of life, covering almost three-fourths of the Earth's surface and existing in both free and combined states.
• Natural water sources include oceans, rivers, and wells.

Composition of Water

• Water is a compound of hydrogen (H) and oxygen (O), with the formula H2O, and not an element.

Water Resources on Earth's Surface

• Snow and frost are natural forms of water in solid state.
• Rainwater is the purest natural form of water, almost free from impurities like oxygen, nitrogen, and carbon dioxide.
• In industrial regions, rainwater can dissolve nitrogen dioxide and sulfur dioxide, forming nitric and sulfuric acids, which cause acid rain.
• River water, lake water, and sea water are impure forms of natural water containing impurities like sand particles, organic matter, bacteria, and mineral salts.
• Sea water is indicated as the most impure form of natural water, including sodium chloride.

Water Resources Below Earth's Surface

• Well water, found above impervious rocky layers, contains soluble impurities.
• Spring water, which forcefully comes out under pressure, contains soluble salts and minerals.

Importance of Water - Basic Uses

• Water is essential for life processes in all plants, animals, and humans, including photosynthesis and excretion.
• Household applications of water are numerous, including washing, cooking, and bathing.
• Water is used for extinguishing fires directly or in fire extinguishers.
• Water is a means for transporting goods via ships.
• Water serves as a habitat for marine life.

Importance of Water - Industrial and Agricultural Uses

• Water generates electricity in hydroelectric power stations.
• It generates steam in boilers for various industries.
• In agriculture, water is important for irrigation, crop production, and as a medium for spraying pesticides.

Three States of Water

• Water exists in three states: solid, liquid, and gaseous.
• On freezing, water exists in the solid state.
• At room temperature, water exists in the liquid state.
• On boiling, water turns into steam or water vapor, existing in the gaseous state.

Occurrence of Water in Different States

• Solid state: as snow and frost.
• Liquid state: in sea water, river water, and lake water.
• Gaseous state: as water vapor in air, depending on climatic conditions.

Change of State of Matter by Water

• Solid state (ice) changes to liquid state (water) through melting.
• Liquid state (water) changes to gaseous state (water vapor) through vaporization.
• Gaseous state (water vapor) changes to liquid state (water) through condensation.
• Liquid state (water) changes to solid state (ice) through freezing.

Interchange of the Three States of Water

• Ice (solid state) on melting changes to water (liquid state).
• Water (liquid state) on heating changes to steam (gaseous state).
• Steam (gaseous state) on condensation gives back water (liquid state).
• Water (liquid state) on freezing gives ice (solid state).

Water Cycle

• The water cycle is a natural process by which the circulation of water takes place from the Earth's surface to the atmosphere and back as rainwater.

Water Cycle Processes

• Evaporation occurs when the sun's rays warm the Earth's surface and evaporate water from streams, rivers, and the sea.
• Respiration by living organisms contributes to water vapor.
• Burning of fossil fuels releases water vapor.
• Water vapor rises, condenses at higher altitudes into small droplets, forming clouds.
• Clouds float in the atmosphere, and as water droplet size increases, they fall back to Earth as rain.
• Rainwater flows into streams, which enter rivers and seas.
• River and sea water evaporates, forming clouds, thus continuing the cycle.
• The water cycle balances water in nature and helps regulate weather conditions.

Water as a Solvent

• Water is a universal solvent as it dissolves a large number of substances, including sugars, salts, and gases like ammonia and hydrogen chloride.

Solvent, Solute, and Solution

• A large number of substances dissolve in water.
• The substance that dissolves in a liquid to form a solution is called a solute (e.g., sodium chloride).
• The liquid or medium of dissolution allowing the solute to dissolve is the solvent (e.g., water).
• A homogenous mixture of a solute in a solvent is a solution.
• Examples include sodium chloride, copper sulfate, and ferrous sulfate dissolving in water. Charcoal floats on water, while kerosene forms a layer on water.

Potable Water

• Potable water is fit for human consumption.
• Potable water should be clear, colorless, free from harmful germs and harmful salts, and have a good taste.

Types of Water not Considered Potable

• Distilled water is completely free from dissolved salts, potentially causing deficiency when consumed as it can dissolve salts from the human body.
• Seawater contains high percentages of dissolved salts such as sodium chloride, calcium, and magnesium, making it unsuitable for drinking and agricultural purposes.

Need for Potable Water

• Even though the Earth's surface is covered with water, only a small percentage is safe for drinking and household purposes.

Purification of Water

• Purification removes dissolved minerals (e.g., calcium & magnesium salts), gases (e.g., carbon dioxide), suspended impurities (e.g., sand, organic matter), and disease-causing germs (e.g., bacteria causing diarrhea, typhoid).
• In cities from rivers & lakes water is received and may not potable.
• Water is purified in a purification plant before it enters individual homes through water taps.
• Boiling water and using water filters are common household methods for obtaining pure drinking water.
• Distillation removes impurities from, obtaining pure water in the laboratory or by using a distillation still.

Removal of Impurities from Water

• Suspended impurities are removed through sedimentation and decantation or filtration.
• Chemical used in sedimentation is alum and lime where particles coagulate and settle down.
• Filtration involves passing water through sand and gravel to remove the suspended particles.
• Chlorine or bleaching powder are the chemicals used in purification to remove harmful germs.

Water Pollution

• Water pollution is contamination of water by various pollutants like bacteria, viruses, domestic sewage, and industrial chemicals.

Types of Water Pollutants

• Chemical pollutants are from industrial chemicals (paints, textiles, and dye stuff industries).
• Thermal pollution - high heat discharge into water bodies.

Disease-Causing Water Pollutants

• Human and animal excreta contaminate water with bacteria and harmful micro-organisms, causing water-borne diseases.

Steps to Avoid Water Pollution

• Harmful wastes should not enter into the water and proper sewage systems must be used to prevent human excreta from entering water sources.
• Washing clothes and bathing should be avoided near water sources.
• Planting trees near water sources minimizes pollution.
• Water should be cooled before being discharged as waste.
• Awareness programs on the effects of water pollution and ways to control it should be conducted using various media.

Conservation of Water - Need

• With only a small percentage of water on earth fit for human consumption, it is important to conserve it.

Conservation of Water - Meaning

• Conservation of water means preventing its wastage, so clean water can be obtained by preventing pollution.

Conservation of Methods - Methods

• Water can be recycled after industries and use it for other reasons.
• Rainwater must be harvested to prevent wastage.
• Dams may be constructed for adequate water collection.
• Drip irrigation may be used in agriculture, and pollution of rivers must be checked.
• Wells should be covered to prevent washing and cleaning nearby.
• Water-saving devices must be used as in homes, such as closing running water and checking pipes.