Water Analysis: pH Determination

The pH test is an important preliminary test. (see pH) Small changes in pH (0.3 units or even less) are usually associated with relatively large changes in other water qualities. Most natural waters will have pH values from pH 5.0 to pH 8.5. the acidic, freshly fallen rain water may have a pH value of 5.5 to 6.0. If it reacts with soils and minerals containing weak alkaline materials, the hydrogen ion concentration will decrease. The water may become slightly alkaline with a pH of 8.0-8.5. Waters more acid than 5.0 and more alkaline than 8.5 to 9.0 should be viewed with suspicion. Sudden changes in pH values serve as warning signals that water quality may be adversely affected through the introduction of contaminates.

pH of water samples can be determined in the field or the samples can be collected and pH determined later. Since most aquatic systems have a pH in the midrange of pH scale, an indicator with a pH from 5-9 may be adequate. However, a wide range indicator is often the best to start with.

Place a small amount of the water sample in a test tube or other container. Add one or two drops of indicator to the sample. After 30 seconds compare the color of the water/indicator solution to the color chart provided with the indicator. Read the pH of the sample from the chart. Indicator paper can also be used.

Healthy pH Ranges for Aquatic Life

  • Bacteria 1.0---------------------------------------------13.0
  • Plants (algae or rooted) 6.5----------------------12.0
  • Carp, sucker, catfish, some insects 6.0--------9.0
  • Bass, Crappie 6.5------8.5
  • Snails, clams, mussels 7.0-----9.0
  • Most animals (trout, mayfly, stone fly, caddis fly) 6.5-----7.5