WATER

Water on the Earth occurs in three main states:

• Solid e.g. ice, snow, hail, frost.
• Liquid e.g. dew, rain.
• Vapour e.g. mist, steam and clouds.

About 97% of all the water on the Earth is salty water while only 3% is fresh water.

1. Salty water 97%
2. Fresh water 3%
   • Atmospheric water 0.001%
   • Surface water 0.03%
   • Ground water/ underground water 0.90%
   • Glacial ice 2.06%

Main sources of water

1. Surface water include rivers, streams, lakes and ponds
2. Ground water/underground water. It is held in the underground layer of water-bearing rock called aquifer. Underground water can be obtained through artificial means (wells) or natural means through springs
3. Rain water. It can be collected from roofs and other hard surfaces and stored for uses.

Water cycle (hydrological cycle)

1. Evaporation.
2. Condensation
3. Precipitation
4. Collection

Evaporation
This occurs when the heat from the sun causes water from oceans, lakes, rivers and other water bodies to change from liquid to vapour and rise into the atmosphere.

Plants also lose water through their leaves by the process of transpiration. Plants absorb water from the soil through their roots and then release it through tiny openings called stomata on their leaves.

Condensation
As the water vapour rises into the atmosphere, it cools down and condenses into tiny water droplets or ice crystals. This process forms clouds in the sky.

Precipitation
When the water droplets in the clouds combine and become too heavy, they fall back to the Earth's surface as precipitation.

Precipitation can take various forms, including rain, snow, sleet or hail.

Collection
This takes place when water falls back to Earth as precipitation.

Some water that falls on the ground forms run-off which collects into streams, oceans, lakes, rivers.

Some of water falls on land, which normally soaks into the soil and become part of the groundwater (groundwater usually is held in layers of rock called aquifers). The cycle starts all over again.

Importance of Water Cycle (Hydrological Cycle)

1. Sustaining life: The water cycle ensures the continuous availability of fresh water, which is essential for all living organisms, for drinking, agriculture, sanitation, and various biological processes.
2. Climate regulation: The water cycle plays a crucial role in regulating the Earth's climate by distributing heat around the planet through processes like evaporation, condensation, and precipitation, which are essential for maintaining global temperature patterns and weather systems.
3. Supporting ecosystems: The water cycle provides the necessary water for plants and animals. It maintains the balance of fresh water in rivers, lakes and wetlands which are habitats for various species. Healthy ecosystem, in turn, support biodiversity and provide essential services such as pollination and nutrient cycling.
4. Agricultural productivity: Agriculture relies heavily on the water cycle. Rainfall provides the water needed for crop growth, while irrigation systems often depend on natural water sources replenished by the cycle. The availability of water through the water cycle therefore increases the agricultural productivity.
5. Replenishing freshwater sources: The water cycle continuously replenishes freshwater sources such as rivers, lakes and groundwater. This replenishment is important for human consumption and industrial use.
6. Soil nutrient distribution: Water cycle facilitates the movement of nutrients and organic matter. Precipitation and surface runoff distribute these nutrients across different regions, promoting plant growth and soil fertility.

More on the importance of hydrological cycle.

PROPERTIES OF WATER

1. Physical Properties
1. It is colourless, odourless and tasteless.
2. It is the only substance that occurs naturally in all the three states of matter.
3. Pure water freezes at 0◦C and boils at 100◦C.
4. Pure water is neutral, it is neither an acid nor a base.
5. It dissolves more substances than any other liquid and is usually called the Universal Solvent.
6. It has a high surface tension.
7. It has a high specific heat index.
2. Chemical properties of water

1. Cold water reacts with some metals to form metal hydroxide and liberates hydrogen gas.
Potassium + water →potassium hydroxide + hydrogen
This reaction is very dangerous to be attempted in the chemistry laboratory.
2. Steam reacts with some metals to form respective metal oxide and hydrogen gas.
These metals are like, magnesium and iron.
Magnesium + steam → magnesium oxide + hydrogen
3. Water reacts with some gases to form acids.

Eg. Sulphur dioxide(gas) + water → sulphurous acid
Carbon dioxide(gas) + water →carbonic acid

Chemical tests of water

1. Water turns the white colour of anhydrous copper (II) sulphate to blue
   CuSO₄(white) + 5H₂O → CuSO₄.5H₂O(blue)
   
2. Water turns the blue cobalt (II) chloride to pink
   CoCl₂(blue) + 6H₂O → CoCl₂.6H₂O (pink)

Water treatment and Water Purification

At household level, water can be treated or purified by the following methods:

• Boiling. Boiling water helps to kill disease-causing organisms such as bacteria because these micro-organisms cannot tolerate high temperature (elevated temperature). After being boiled the water is usually left to cool and filtered using a clean cloth.
• The use of commercial filters. The water is passed through ceramic element which contains pores. Once poured into ceramic element, the contaminated water is slowly passed through the pores and is collected in the lower container. The tiny pores allow water to pass through but trap large particles and some pathogens like bacteria and viruses.
• The use of chemical purifier. This involves disinfection of water by using chemicals which are in form of tablet or liquid. These kill or inactivate the bacteria, viruses and other pathogens in water, example of purifiers are water guard and AquaGuard.
  To use it, a recommended amount of the purifier is put in a specific amount of water in a container. Water is shaken or stirred well then left to settle for some time before it can be safe for drinking.

Simple Filter

Simple filter is made up of

• Gravel – traps any floating substances.
• Sand – ensures even the small suspended particles do not pass through.
• Charcoal – kills some of the harmful bacteria.
• Clean cloth – filters every tiny particles.

URBAN WATER TREATMENT

1. Coagulation and flocculation: in this stage, chemicals such as alum (aluminium sulphate) and iron III sulphate are added to the water to bind together small particles present in water and form large particles called flocs.
2. Sedimentation: the water is then allowed to settle in a sedimentation tank, where the flocs settle to the bottom of the reservoir and are removed.
3. Filtration: the water is then passed through filters made of sand, gravel and charcoal to remove any remaining particles and impurities.
4. Disinfection: In this stage, chemicals, such as chlorine or ozone or sodium hypochlorite are added to the water to kill any remaining bacteria, viruses and other microorganisms.
5. Storage: the treated water is then stored in reservoirs or tanks before being distributed to homes and industries.

Importance of water treatment

1. Prevents water borne diseases as bacteria and other parasites are killed during the process.
2. It removes particles suspended in water.
3. It is suitable in factories, laboratories and other medical fields as materials manufactured in these areas require high degree of purity.

USES OF WATER

1. Economic uses
• It is used in generating electricity (HEP).
• It is used in agriculture for irrigation.
• In mining it is used to wash away impurities associated with minerals.
• Habitat for fishes, therefore fishing activities are possible in the presence of water.
2. Domestic uses
In homes, water is used for:
• drinking,
• cooking food
• washing utensils and clothes.
• bathing
3. In industries
• Water is used for cooling hot machine parts
• Used as solvent to dissolve different substances.
• Cleaning equipments
4. Medical uses
• Washing wounds at hospitals.
• Making medicine solutions.
• Cleaning equipments.
• Sterilization of medical instruments and equipment using boiled water or pressurized steam to kill bacteria, viruses and other microorganisms
• Drip preparation.
• Used by patients in drinking tablets.

UNIQUE PROPERTIES OF WATER

1. Absorption of infrared radiation (heat).
It has ability of absorbing radiation from the sun. As a result of this, the water bodies such as oceans act as heat reservoirs and are able to emit this heat to the Earth’s surface.
2. High specific heat capacity
It is the amount of heat energy that is needed to increase the temperature of a substance by one degree. It is a property of a substance that determines how much heat is needed to change its temperature. Water has a high specific heat capacity, meaning that it can absorb and store a large amount of heat without a significant change in temperature. For example a metal of a pot that is used in boiling water heats up very quickly to the extent of burning anyone who touches it while the water may take several minutes before its temperature increases even slightly.
3. Less dense solid state of water.
This is another unusual property of water. Ice which is the solid state of water is less dense than its liquid state. Put an ice into water to verify by yourself. You will find that the ice does not sink to the bottom of the glass, but floats on top of the liquid. While other substances contract when they solidify water expands, its molecules arrange in a crystalline structure with large spaces between them. This arrangement causes the ice to have a larger volume than the liquid water, which results in the ice being less dense.

Form Two topics