IGCSEChemistryCIERevision Notes10. Chemistry of the Environment10.1 Water & Water Pollution10.1.2 Substances in Water from Natural Sources

Substances in Water from Natural Sources (CIE IGCSE Chemistry)

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Substances in Water from Natural Sources

  • We use water in many aspects of our everyday life:
    • Domestic uses: for drinking, cooking, gardening and general sanitation 
    • Agricultural uses: as a drink for animals and watering crops
    • Industrial uses: as a solvent, as a coolant and heated to make steam used to generate electricity
  • Water is found in natural sources such as lakes, rivers and underground water sources (groundwater)
  • A rock that stores water is known as an aquifer
  • Water from natural sources may contain a variety of different substances, including:
    • Dissolved oxygen
    • Metal compounds
    • Plastics
    • Sewage
    • Harmful microbes
    • Nitrates from fertilisers
    • Phosphates from fertilisers and detergents
  • Many of these substances enter water sources when rain falls and washes them into lakes, rivers or groundwater
  • Some of these substances are naturally occurring but many are a direct result of human activities

Exam Tip

Despite the term 'natural source’, water from these sources may contain lots of impurities and harmful substances and should not be confused with water which is clean and ready for use.

Beneficial & Harmful Substances in Water

  • Some of the substances which may be found in natural water sources are beneficial and others may have harmful effects
  • Beneficial substances include:
    • Dissolved oxygen - essential for aquatic life
    • Metal compounds - some provide essential minerals which are necessary for life, such as calcium and magnesium
  • Potentially harmful substances include:
    • Metal compounds - some are toxic like aluminium and lead
    • Some plastics - these may be harmful to aquatic life in many ways, e.g. getting trapped in plastic waste, dying of starvation as their stomach is filled with plastic
    • Sewage - contains harmful microbes which can cause disease 
    • Nitrate & phosphates from fertilisers - these can promote the growth of aquatic plant life which leads to deoxygenation of water. Ultimately, this can cause damage to aquatic life in a process called eutrophication (you do not need to know the details of this process)

Exam Tip

Metal compounds can be both beneficial and harmful, it depends on the metal within the compound, e.g. calcium, magnesium, potassium and sodium are all metals which are essential for life. Harmful metals include lead, arsenic and mercury.

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    Caroline

    Author: Caroline

    Caroline graduated from the University of Nottingham with a degree in Chemistry and Molecular Physics. She spent several years working as an Industrial Chemist in the automotive industry before retraining to teach. Caroline has over 12 years of experience teaching GCSE and A-level chemistry and physics. She is passionate about creating high-quality resources to help students achieve their full potential.