This is because the surface water exists in nature, the majority do not apply directly, because there may be some substance or germs get mixed, different causes of disease and harm the health of the user.
This is because the water that exists in nature mainly suited to be used directly. You may have some substance or a mixture of various bacteria which cause the disease and harm the health of water users.
This is because the surface water existing in the nature mainly is used directly. It may have some substances or various pathogens mixed, which will cause the disease and is harmful to the health of water users.