This Link does not exist in your language, View in: 汉语 (zh), Español (es), Français (fr), English (en),
Or use Google Translate:

Water is essential for life. The amount of fresh water on earth is limited, and its quality is under constant pressure. Preserving the quality of fresh water is important for the drinking-water supply, food production and recreational water use. Water quality can be compromised by the presence of infectious agents, toxic chemicals, and radiological hazards.