pH testpH units and range.Definition: pH is a measurement of how acidic or basic the water is. It is measured on a logarithmic scale (like the Richter scale for earthquakes) so every unit represents a 10 fold change in acidity. The scale ranges from 0-14, where 7 is neutral, lower numbers are increasingly acidic and higher numbers are increasingly basic.

    Why we monitor pH: pH affects many chemical and biological processes. Many organisms are adapted to a specific pH range.

    What influences pH: Rainfall is naturally somewhat acidic, so pH may be influenced by recent precipitation. The types of rock and soils that runoff passes over and through also play an important roll in buffering the water (increasing the pH). Natural geology such as calcareous rocks and soils provide this natural buffering, while granitic rocks do not. Aquatic plants also affect the pH by taking carbon dioxide directly from the water for photosynthesis, which can cause the pH to increase during the day. Human activities such as mining may result in acidic mine drainage due to a chemical reaction between water and rocks containing sulfur bearing minerals.

    Visit our pH information page for more information on natural and human factors that influence pH.


    Methods to measure pH:



    Remove a test strip from the container and then reseal the container

    pH color strips

    Place colored end of test strip in the water for 30 seconds

    stirp in water

    Remove test strip from the water and shake off excess water.  Wait 2 minutes for the strip to fully react 


    Compare test strip to the color guide and select the closest color match. Record the pH

    color compare

    Stream Side Science pH instructions - great for laminating and using with groups.