Book 30, Question 114
Why shouldn't you drink water straight from a clear lake?
Even the cleanest-looking lake or stream can hold tiny germs that you can't see, such as parasites left by animals.
They can give people stomachaches and make them sick for days. Water that looks sparkling is not always safe. That's why campers bring water, or treat lake water by filtering and boiling or using purifying tablets. Always ask a grown-up first.