I´d think twice before I drank that water without means of purifying it. Even without industrial pollution it may be pretty bad. A hot summer day means that the water was pretty warm too. In warm water bacteria and algae grow fast. As that´s what tadpoles feed on there where some for sure. Some algae produce poisons that can make you throw up. So drinking that pond water could promote dehydration.
Tadpoles are not an indicator for unpolluted clean water.