pH Measurement

pH is one of the most common analyses in soil and water testing. An indication of the sample’s acidity, pH is actually a measurement of the activity of hydrogen ions in the sample.

pH measurements are reported on a scale from 0 to 14, with 7.0 considered neutral.  Those solutions with a pH below 7.0 are considered acids, and those between 7.0 and 14.0 are designated bases. The pH scale is logarithmic, so a one unit change in pH actually reflects a ten fold change in the acidity.  For instance, orange juice, pH 4, is ten times more acidic than cottage cheese, which has a pH of 5.

Low pH waters have a tendency to cause corrosion, while high pH waters may contribute to scale formation in, for example, boiler or cooling systems.

Small changes in pH, 0.3 units or less, are usually associated with relatively large changes in other water qualities — the solubility of iron, copper, calcium, manganese, and other metals, and the proportions of carbon dioxide, bicarbonate, and carbonate are greatly changed by small numerical changes in the pH measurement.

pH can be measured visually, through the use of liquid reagents or pH test strips, or electronically, through the use of a pH meter or post-reaction colorimeter. Visual comparisons use pH indicators where color changes reflect the pH, which are then matched to color standards.

pH meters simplify the pH test. An electrode is placed in the sample, and the pH is read directly from the meter. While the meter is very easy to use, the electronics within the meter are complex. After the pH electrode measures the millivolts of potential between the reference electrode and the pH electrode, the meter converts this reading to pH units.

In pools a slightly alkaline pH of 7.4 to 7.6 is most desirable because this range is most comfortable to the human eye and provides for optimum use of free chlorine while maintaining water that is not corrosive or scale forming.

While the ideal pH level of drinking water should be between 6-8.5, the human body maintains pH equilibrium on a constant basis and will not be affected by water consumption. For example, our stomachs have a naturally low pH level of 2 which is a beneficial acidity that helps us with food digestion.