Water should be filtered before it is used for drinking, as it contains many impurities that cannot be easily seen with the naked eye. In order to have safe drinking water, it should be boiled.
Water gets contaminated by humans and it is not safe for drinking.
Drinking contaminated water results in diseases such as cholera, typhoid and diarrhoea. Polluted water can also prove fatal. Please refer Wastewater Story Class 7 Extra Questions for more information.
CBSE Revision Notes 