[Science Form 2] Water

Water is perhaps the most important nutrient in our diets. In fact, a human adult needs to drink approximately two litres (8 glasses) of water every day to replenish the water that is lost from the body through the skin, respiratory tract, and urine.

However, 99.7% of the Earth's water supply is not usable by humans. This unusable water includes salt water, ice, and water vapour in the atmosphere.

Only fresh water, which is contained in rivers, lakes, and underground sources, can be used for human consumption. Furthermore, many freshwater sources are not suitable for human to drink.

Water containing dangerous microorganisms and large amounts of industrial waste or agriculture chemicals (eg pesticides) can be toxic and unfit for drinking. Hence, humans have a great need for a reliable source of clean fresh water for drinking.

In addition to the water needed for drinking, other uses of fresh water include household use (eg cooking and cleaning), industry, agriculture (eg irrigation), and recreation.

Hence, the quality of fresh water supply is important for virtually every aspect of our lives. Water that is supplied for domestic use must be treated to ensure it is clean.

The water supplied must meet the National Guidelines for the Quality of Drinking Water (1983), which is based on the World Health Organisation (WHO) Guidelines for the Quality of Drinking Water (1984).