There is no such thing as naturally pure water. In nature, all water
contains some impurities. As water flows in streams, sits in lakes, and
filters through layers of soil and rock in the ground, it dissolves or
absorbs the substances that it touches. Some of these substances are
harmless. In fact, some people prefer mineral water precisely because
minerals give it an appealing taste. However, at certain levels, minerals, just
like man-made chemicals, are considered contaminants that can make
water unpalatable or even unsafe.