Chapter 14 — Water

Definition and general properties
Water is a simple compound made of hydrogen and oxygen that appears as a clear, colourless, and generally tasteless liquid at normal temperatures. It is found in nature in large amounts and is essential for all living things. Water has some special properties: it can flow easily, it can stick to other surfaces (adhesion), it can carry substances dissolved in it, and it helps keep living things cool by absorbing heat.

Role in living things
Every cell needs water to carry out processes such as moving nutrients, removing wastes, and carrying out chemical reactions. Plants use water in photosynthesis, animals and humans drink water to stay alive, and water helps keep bodily temperature steady. Without water, seeds cannot germinate and cells cannot function, so life on Earth depends on water.

Role in nature and human life
Water shapes landscapes through rivers and rain, providing habitats for many creatures. It supports agriculture by irrigating crops, and it is used in factories to make goods and in households for cooking, washing and cleaning. Water is also important for recreation and for generating some forms of energy, like hydroelectricity.

Importance of safe water
Not all water is safe to drink. Clean water prevents many diseases and is needed for good hygiene. Communities work to provide safe sources of water through wells, taps and treatment plants. Understanding the value of water helps people avoid wasting it or polluting it, which keeps the water usable for future needs and supports healthy living.

Daily examples
Examples include drinking water after playing, watering a garden, using water to clean utensils, and boiling water to kill germs. Simple habits like storing water in covered containers, turning off taps when not in use, and using water carefully show how important water is in daily life and how we can protect it.

Where water comes from
Water on Earth exists in different places. The main sources are rain, rivers, lakes, ponds, glaciers, groundwater stored in soil and rocks, and oceans. Rain is the primary way fresh water is added to rivers and groundwater. Oceans hold most of Earth’s water, but their salt content makes them unsuitable for drinking and most farming without treatment.

Surface water: rivers, lakes and ponds
Surface water is water that collects on the land. Rivers flow over land and connect high areas to lower areas, often ending in lakes or oceans. Lakes and ponds hold water in basins. People draw water from rivers and lakes for drinking, irrigation and industry. Dams are built on rivers to store water in reservoirs that supply cities and farms during dry periods.

Groundwater: wells and springs
Some rainwater soaks into the ground and fills spaces between soil and rocks; this stored water is groundwater. Wells and borewells reach down to groundwater and bring it to the surface. Springs occur where groundwater naturally flows out. Groundwater is important because it can be used when surface water is not available, but it can be slow to refill if overused.

Rain and glaciers
Rain replenishes rivers and groundwater. In mountainous regions, snow and glaciers store water as ice that melts slowly, supplying rivers during warmer months. Changes in snowfall and glacier size can affect water supplies for many people.

Human-made sources
People also create water sources, such as ponds, tanks and rainwater harvesting systems. Collecting rainwater from roofs into barrels or tanks helps supplement household water supplies and reduces pressure on other sources.

Safe use considerations
Not all sources are equally safe. Pond and river water may contain germs, and groundwater can be contaminated by chemicals leaching from soil. Recognising the source helps choose correct treatment methods such as filtration or boiling to make water safe for use.

Overview of states
Water can exist in three physical states: solid (ice), liquid (water), and gas (water vapour). The state depends on temperature and pressure. At normal conditions on Earth, we most often see water as a liquid, but in cold climates or freezers it becomes solid, and when heated it becomes vapour.

Solid state: ice
When water is cooled to 0°C or below (at normal pressure), it changes into ice. Ice has a fixed shape and the particles are arranged in a rigid lattice. Ice takes more space than the same mass of liquid water: that is why ice floats on water. Ice is found naturally in polar regions, in glaciers, and on high mountains. When ice melts, it absorbs heat and turns back into liquid water.

Liquid state: water
Liquid water flows and takes the shape of its container. The particles in liquid water are close but move past each other, allowing flow. Most life processes occur in liquid water. The temperature range at which water stays liquid depends on pressure, but for daily learning we use 0°C–100°C at sea level as a useful guide.

Gaseous state: water vapour
When water is heated it can change to gas, called water vapour. This happens during boiling or evaporation. Water vapour is invisible; we see clouds or steam as tiny liquid droplets formed when vapour cools. Water vapour mixes with air and is part of humidity. Condensation of vapour produces dew and clouds.

Changes between states
Common processes: melting (solid→liquid), freezing (liquid→solid), evaporation (liquid→gas), and condensation (gas→liquid). These changes can be reversed. Heat is needed to melt and evaporate, while cooling causes freezing and condensation. Everyday examples include ice cubes melting, puddles drying up, and steam forming over a hot vessel.

Importance for life and weather
State changes of water affect weather, climate and living systems. Evaporation cools surfaces, and condensation releases heat into the atmosphere, influencing winds and rainfall. Understanding these states helps in practical tasks like storing food, cooking, and preserving water during cold seasons.

What is evaporation?
Evaporation is a process where liquid water changes into water vapour, a gas. This happens at the surface of the liquid when some molecules gain enough energy to escape into the air. Evaporation occurs at all temperatures though it is faster when the temperature is higher, when the air is drier, and when wind moves the air above the water surface. Evaporation is the reason wet clothes dry, puddles shrink, and water from soil returns to the atmosphere.

Factors affecting evaporation
Several factors control the rate of evaporation: temperature (higher temperature increases evaporation), surface area (a larger surface area speeds up evaporation), wind (which removes humid air from the surface), and humidity (high humidity slows evaporation because the air already contains a lot of water vapour).

What is condensation?
Condensation is the opposite process: water vapour cools and changes back into liquid droplets. When warm, moist air meets a cold surface or when it rises and cools, water vapour condenses to form tiny droplets. These droplets make fog, mist, dew and clouds. You can see condensation when water appears on a cold glass of water or on a bathroom mirror after a hot shower.

Everyday and natural examples
Evaporation: drying clothes in sunlight, loss of moisture from soil, sweating that cools the body. Condensation: dew on grass early in the morning, fog over fields, and cloud formation high in the sky. In the kitchen, steam from cooking can condense on a lid or window.

Importance in the water cycle and life
Evaporation and condensation are key links between water on Earth and water in the air. Evaporation from oceans and land returns water to the atmosphere; condensation forms clouds that bring rain. These processes help clean water as it moves through the cycle and maintain the balance of moisture needed for plants, animals and humans. Simple classroom experiments—like leaving a dish of water in sun versus shade, or collecting droplets on a cold lid held above boiling water with adult help—make these processes visible and easy to understand.

Definition and overview
The water cycle is the continuous movement of water between the Earth's surface, the atmosphere and below the ground. It is powered mainly by the Sun’s heat and involves several repeating steps: evaporation, transpiration, condensation, precipitation and collection. This cycle does not have a beginning or end; it keeps water moving and renewing the supply of fresh water in different places.

Evaporation and transpiration
Sunlight warms water in oceans, lakes, rivers and soil, causing evaporation — water turning into vapour. Plants also release water vapour through tiny pores called stomata in a process called transpiration. Together these processes are often called evapotranspiration and they send water into the atmosphere as vapour.

Condensation and cloud formation
As warm moist air rises, it cools. Cooling causes water vapour to condense into tiny liquid droplets that join to form clouds. Condensation changes invisible vapour into visible droplets and releases heat into the air, which influences weather patterns and air movement.

Precipitation
When droplets in clouds become large enough, gravity pulls them down as precipitation — rain, snow, sleet or hail depending on temperature. Precipitation returns water to the land and sea, supplying surface water and refilling groundwater.

Collection and groundwater recharge
Precipitated water collects in rivers, lakes and oceans, and some soaks into the ground to recharge aquifers and groundwater. Some water moves over land as runoff, eventually flowing into streams and rivers. Human activities, like building roads and houses, change how much water soaks in and how much runs off.

Why the water cycle matters
The water cycle distributes heat and moisture around the planet, affecting climate and weather. It provides freshwater for drinking, farming and ecosystems. Protecting natural areas and using water wisely helps maintain healthy cycles: planting trees, avoiding pollution and harvesting rainwater support recharge and cleaner water for communities.

What are mixtures?
When two or more substances are combined in water, they form mixtures. Mixtures can look different depending on whether the added substance dissolves completely or stays as separate particles. In daily life, many mixtures appear in cooking, cleaning and in nature; distinguishing between types helps decide how to separate and treat them.

Solutions — uniform mixes
In a solution, the solute dissolves completely in a solvent, producing a uniform mixture. Water is a very good solvent for many substances such as sugar and salt. Once dissolved, the solute particles are too small to see and they do not settle on standing. Solutions can conduct electricity if the dissolved substance produces ions (for example, salt water). Temperature often affects solubility: many solids dissolve more in warm water than in cold.

Suspensions — particles that settle
In a suspension, the particles are larger and remain suspended in the liquid for some time but eventually settle down due to gravity. Muddy water is a good example: soil particles make the water cloudy and after standing, the soil settles at the bottom. Suspensions can be separated by filtration, decanting or simply waiting for settling to occur.

Colloids — in between
Some mixtures, called colloids, have particles of intermediate size that do not settle quickly and make the liquid appear cloudy (for example, milk). Colloids are not as easy to separate by simple settling or filtration as suspensions are.

Importance for water treatment
Knowing the difference helps in cleaning water. Suspended dirt can be removed by filtering and allowing to settle, while dissolved substances (like salts) need other treatments such as distillation or special membranes. Everyday examples: making tea (sugar dissolves to form a solution), stirring soil into water (suspension), and using cloth to filter muddy water.

Why purify water?
Water from many natural sources may contain dirt, germs (bacteria, viruses, parasites) and sometimes harmful chemicals. Drinking such water can cause diseases. Simple purification methods used at home and in schools can make water safer to drink and use. Different methods work for different kinds of impurities.

Boiling
Boiling is a reliable and simple method. Bringing water to a rolling boil for one minute (longer at high altitudes) kills most disease-causing organisms. After boiling, water should be cooled in a clean covered container and used or stored safely to avoid recontamination. Boiling does not remove dirt or dissolved salts but makes water microbiologically safer.

Filtration
Filtration removes suspended particles such as sand or mud. Simple filters use layers of cloth, sand and gravel arranged in a funnel or drum. Charcoal can improve taste and reduce some chemicals and smells. Filtration can make water clearer and reduce the load of germs by removing particles that carry microbes. However, very small germs may pass through simple filters.

Solar disinfection (SODIS)
Solar disinfection uses sunlight to reduce microbes. Clear PET bottles filled with transparent water are placed in direct sunlight for six hours or more on a sunny day. UV radiation and heat together reduce bacteria and viruses. This method works best with clear water that has little suspended matter.

Chemical treatment
Adding small amounts of chlorine (bleach) to drinking water can kill many germs if used in correct amounts. Commercial water purification tablets are available. Alum can be used to make suspended particles clump and settle, making water clearer before filtration. Chemicals must be used carefully and following instructions to be safe.

Combining methods
Often a combination is best: first let dirty water settle, then filter through cloth or sand, then boil or use chemical disinfection. Safe storage in clean covered containers prevents recontamination. Communities may use larger treatment plants with sedimentation, filtration and chlorination to supply many people with safe water.

What is groundwater?
Groundwater is water stored beneath the Earth's surface in the tiny spaces between soil particles and in cracks in rocks. After rain or irrigation, some water soaks into the ground and moves downward until it reaches a level where those spaces are filled. This saturated zone contains groundwater that can be used for drinking, farming and other needs.

The water table
The top of the saturated zone is called the water table. The depth of the water table varies with seasons, rainfall, and human use. During rainy months the water table rises as recharge increases; during dry months it goes down. In some places heavy use of groundwater can lower the water table faster than it is recharged, causing wells to dry up.

Wells and borewells
People reach groundwater by digging wells or drilling borewells. Dug wells are shallow and lined with bricks; borewells are deep and reach water in rock layers. Water is drawn up with buckets, pumps or handpumps. Properly constructed wells with covers prevent contamination by surface water or waste.

Springs and artesian wells
Springs occur where groundwater flows out naturally at the surface. An artesian well happens when water under pressure rises by itself through a pipe; this can happen where aquifers are trapped between impermeable rock layers. These natural outlets are valuable sources of fresh water for communities.

Recharge and protection
Recharge means water soaking down to refill groundwater. Activities like planting trees, keeping soil non-compacted and allowing rainwater to soak in help recharge. Urbanisation with roads and concrete reduces recharge by increasing runoff. Pollution from sewage, chemicals and waste can seep into the ground and contaminate groundwater, making it unsafe. Protecting recharge areas and preventing pollution keeps groundwater available and safe.

What is water pollution?
Water pollution occurs when harmful substances such as sewage, industrial waste, agricultural chemicals, oil and trash enter water bodies and make them unsafe. Pollutants can be visible, like plastic and oil slicks, or invisible, like dissolved chemicals and disease-causing microorganisms. Polluted water cannot be used for drinking, bathing, or irrigating food crops without treatment.

Sources of pollution
Common sources include household sewage that is not treated, factory effluent, runoff from agricultural fields carrying fertilisers and pesticides, litter and plastic thrown into rivers and lakes, and oil and chemical spills. In many areas, open defecation and poor sanitation cause direct contamination of water sources. Urban runoff during rains carries rubbish and pollutants into streams and ponds.

Effects on humans and animals
Drinking or using contaminated water causes diseases such as diarrhoea, cholera, typhoid and hepatitis. Polluted water harms aquatic life: toxic chemicals and low oxygen levels can kill fish and other organisms. Polluted water also affects food safety when crops are irrigated with it, and it reduces tourism and recreation value of lakes and rivers.

Environmental changes
Excess fertiliser in water bodies can lead to overgrowth of algae (eutrophication). When algae die and decompose, they use oxygen in water, causing oxygen levels to drop and killing fish. Plastics and other debris harm birds and fish. Oil coats surfaces and suffocates animals and plants. Long-term pollution changes ecosystems and reduces biodiversity.

Prevention and control
Preventing pollution is better than treating it later. Actions include treating sewage before release, using fewer chemicals in farming, proper disposal and recycling of waste, cleaning up spills quickly, and educating communities about not throwing garbage into water bodies. Simple local actions—covering drains, stopping open defecation, and organising community clean-ups—help protect water and health for everyone.

Domestic uses
In every household, water is used for drinking, cooking, cleaning, washing clothes, bathing, and flushing toilets. Safe water is most critical for drinking and cooking because these uses require the cleanest water. Clean water for handwashing helps prevent disease, while water used for cleaning and washing may be reused safely for other purposes like gardening.

Agricultural uses
Farming is the largest user of water in many regions. Irrigation supplies water to crops when rainfall is insufficient. Different crops need different amounts of water; rice fields require more water than millet. Methods like flood irrigation, sprinkler systems and drip irrigation help supply water; drip irrigation is more efficient and reduces waste.

Industrial uses
Industries use water to manufacture goods, cool machines, clean equipment, and as an ingredient in products. Many factories produce wastewater that must be treated before being released to avoid pollution. Recycling water within factories reduces demand for fresh water and lowers pollution.

Energy and transport
Water is used to generate electricity in hydroelectric plants. It also supports transport by rivers and canals and enables fisheries that provide food. Maintaining clean water ensures these services continue to support communities.

Recreation and cultural uses
People use water for swimming, boating and cultural rituals. Maintaining clean and safe water bodies is important for health and for keeping traditions and livelihoods alive.

Planning and wise use
Knowing where and how much water is used helps families and communities plan for supply. Simple steps like fixing leaks, using water-saving methods in agriculture, and reusing water where safe, can reduce demand and ensure everyone has access to the water needed for life and livelihoods.

Need for conservation
Although water covers most of the Earth, usable fresh water is limited. Many places face shortages during dry seasons. Conserving water saves money, protects the environment and ensures future supplies. Small changes in daily habits and community planning can lead to large savings.

Simple actions at home
Fix leaking taps and pipes quickly — a small drip can waste many litres every day. Use a bucket for washing vehicles and avoid running hoses. Take short showers or use a mug to bathe. Turn off the tap while brushing teeth or soaping hands. Use full loads in washing machines and dishwashers. Collect water used for washing vegetables and reuse it for watering plants if it is soap-free.

Rainwater harvesting and reuse
Collecting rainwater from roofs into barrels or tanks provides free water for gardens and cleaning. Recharge pits and soakaways allow rain to soak into the ground and replenish groundwater. Reusing greywater (wastewater from baths and sinks) for flushing toilets or irrigation reduces fresh water demand when done safely.

Community and school actions
Schools can teach water-saving habits, check taps and cisterns regularly for leaks, and install water-efficient fixtures. Communities can protect local water sources, prevent pollution, and support small-scale rain harvesting. Public awareness campaigns and local rules help reduce water waste.

Smart gardening and agriculture
Choose drought-resistant plants and water gardens early in the morning or late evening to reduce evaporation. In agriculture, using drip or sprinkler irrigation and scheduling watering according to crop need saves large amounts of water compared to flood irrigation.

Long-term benefits
Conservation reduces the stress on rivers and groundwater, helps maintain ecosystems, and lowers the energy cost of pumping and treating water. Practising conservation habits builds responsibility in children and prepares communities for dry seasons and climate changes.

Clean water and disease prevention
Access to clean water and good hygiene practices go together to protect health. Contaminated water carries germs that cause diseases such as diarrhoea, cholera, typhoid and hepatitis. Safe drinking water, proper sanitation and hygiene reduce the spread of these diseases and improve community health.

Handwashing and personal hygiene
Washing hands with soap and water at key times — before eating, after using the toilet, after handling animals, and before preparing food — removes germs and prevents infections. Teach the correct handwashing steps: wet, lather with soap for about 20 seconds, scrub all parts of hands, rinse and dry. Keeping nails short and clean also reduces dirt and germs.

Safe water storage
Even clean water can become unsafe if stored improperly. Use clean, covered containers for storing drinking water. Avoid dipping hands or dirty cups into the storage container; use a ladle or a tap. Clean containers regularly and protect them from flies and dust to reduce contamination risk.

Sanitation and community measures
Proper toilets and sewage treatment prevent human waste from polluting water sources. Open defecation leads directly to water contamination in many places. Building and using toilets, and ensuring sewage is treated or safely disposed, protect water for everyone. Vaccinations, regular health checks and keeping surroundings clean also reduce disease risk.

Water quality checks and boiling
If unsure about water quality, boiling water is a safe measure to kill most germs. Chemical treatment or filtration may be needed for certain pollutants. Regular community testing helps identify unsafe sources so corrective action can be taken. Teaching children and families how to make water safer at home saves lives and supports healthy communities.

Why do experiments?
Simple, safe experiments help students see how water behaves and how common processes like evaporation, condensation, filtration and dissolution work. Hands-on activities build observation skills, teach careful recording, and connect ideas to everyday life. Use basic materials and follow safety rules, especially when heating water; always have adult supervision for boiling or hot experiments.

Evaporation test
Place equal amounts of water in two shallow dishes. Put one dish in direct sunlight and the other in shade. Measure water levels at set times (for example every two hours) to see which loses more water. Students record temperature, wind and time of day to understand factors that speed evaporation.

Condensation test
With adult help, boil water in a pan and hold a cold metal lid or plate above the steam. Watch droplets form on the lid—this shows vapour turning back into liquid. Collect the droplets and explain condensation. A safe alternative is to compare a cold and a warm glass of water on a humid day and observe droplets forming on the cold glass.

Filtration and settling
Make muddy water by mixing soil and water. Let one portion stand to settle and filter another through layers of cloth, sand and gravel set in a funnel. Compare clarity of water after each step. Discuss why settling helps and why filtration removes suspended particles but not dissolved salts.

Dissolving and solutions
Mix sugar in one cup of water and sand in another. Stir both and observe that sugar dissolves and disappears while sand remains visible. Leave both to stand and note settling. This activity shows the difference between solutions and suspensions and leads to discussion on how to make water safe.

Recording and conclusions
Encourage drawing diagrams, noting observations, and explaining results in simple sentences. Use these experiments to link theory to real life: drying clothes, boiling water to make it safe, and filtering muddy water are everyday applications of observed processes.