• Like air, water is also essential for life.
• Water is the only substance on Earth that is in liquid form at the temperatures commonly found on the surface of our planet.
Figure 6: Water is in liquid state on the surface of the Earth
• Water is a universal solvent, i.e. most of the substances can be easily dissolved into it.
• This allows water to carry nutrients to cells, and carry waste away from them.
• In addition to this, water has the unique property of expanding as it freezes.
• The water that we use mainly comes from rivers, ponds, lakes, and wells.
• Often sand, dirt, mud, germs, etc., make this water unfit for consumption. We call these substances impurities.
Impurities are of two Kinds:
• Soluble impurities are the ones that dissolve in water (e.g., salt)
• Insoluble impurities are the ones that do not dissolve in water (e.g., sand and germs).