Substances in Water from Natural Sources (Cambridge (CIE) IGCSE Chemistry)

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 ions (E.g. Ca²⁺, K⁺, Na⁺, Mg²⁺)

  • 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

Photo by Ben Clayton on Unsplash 

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)