Background Information
pH measures the relative acidity of the water.  A pH level of 7.0 is considered neutral.  Pure water has a pH of 7.0.  Water with a pH level less than 7.0 is considered to be acidic.  The lower the pH, the more acidic the water.  Water with a pH greater than 7.0 is considered to be basic or alkaline.  The greater the pH, the greater its alkalinity.  In the US, the pH of natural water is usually between 6.5 and 8.5.  Fresh water sources with a pH below 5 or above 9.5 may not be able to sustain plant or animal species. 

Industries and motor vehicles emit nitrogen oxides and sulfur oxides into the environment.  When these emissions combine with water vapor in the atmosphere, they form acids.  These acids accumulate in the clouds and fall to earth as acid rain or acid snow.  Acid rain damages trees, crops, and buildings.  It can make lakes and rivers so acidic that fish and other aquatic organisms cannot survive. 

Test Procedure
To perform the pH test, use a pH test kit or pH paper.  Follow the instructions provided with the kit.  pH must be measured immediately at the test site because changes in temperature affect pH value.  Try to take the water sample at a location away from the bank and below the water surface.  pH is recorded with a number value only, there are no units associated with the pH value.  

What to Expect
A pH reading between 6.5-7.5 is considered to be excellent; the water is neutral.  A pH level between 6-6.4 or 7.6-8.0 is considered to be good.  A pH level between 5.5-5.9 or 8.1-8.5 is considered to be fair.  If the water's pH level is less than 5.5 it is very acidic and is at a level where fish and other organisms may find it impossible to survive.  A pH level greater than 8.6 is considered to be very alkaline and this is not good either. 

NOTE: Please consider using the Sense of Scale activity when learning about pH.