The pH of a sample of water is a measure of the concentration of
hydrogen ions. The term pH was derived from the manner in which
the hydrogen ion concentration is calculated it is the negative
logarithm of the hydrogen ion (H+) concentration. What this
means to those of us who are not mathematicians is that at
higher pH, there are fewer free hydrogen ions, and that a change
of one pH unit reflects a tenfold change in the concentration of
the hydrogen ion. For example, there are 10 times as many
hydrogen ions available at a pH of 7 than a pH of 8. The pH
scale ranges from 0 to 14. A pH of 7 is considered to be
neutral. Substances with pH less than 7 are acidic; substances
with pH greater than 7 are basic. The pH of water determines the
solubility (amount that can be dissolved in the water) and
biological availability (amount that can be utilized by aquatic
life) of chemical constituents such as nutrients (phosphorus,
nitrogen, and carbon) and heavy metals (lead, copper, cadmium,
etc.). For example, in addition