The Water Supply Department in HK generally provide good clean water with their purification facilities. Chlorine is also added to water for sanitary purposes. However it is not uncommon that the water pipes emit lead, zinc and copper to the water.
Natural water is not pure. Chemically pure water (H2O) consists of the two elements hydrogen and oxygen. In nature, chemically pure water however does not exist. Rainwater absorbs various substances from the atmosphere, e.g. CO2 and as part of the water cycle, it then flows through the soil layers and becomes enriched with further ingredients. The water hardness varies from region to region.