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Understanding the pH Scale in Water Monitoring
Wednesday, November 26, 2014

If you think back to your middle school science days, it's hard to forget experiments involving the pH scale, levels, and values. Probably your first experience into the science of pH involved taking a piece of litmus paper. If you put a lemon on the litmus paper, it turned red, and if you used soapy water on it, the paper turned blue.

How to Measure pH

The pH value of a substance is an indicator for acidity, alkalinity, or basic. The pH scale is a measurement of hydrogen ions in a solution and ranges from 0-14. Furthermore, a pH value of 7 puts a substance at neutral. The lower you go on the number scale, from 0-6, indicates acidity, and a higher value, 8-14, is an indication of alkalinity and has a lower number of hydrogen ions. Each whole pH value below 7 is ten times more acidic than the next higher value and vice-versa with basic substances.

A few examples to help you understand the pH scale:

  • Apple Juice – 3

  • Orange Juice – 3.5

  • Coffee – 5.5

  • Milk – 6.2

  • Baking Soda – 8.5

  • Soapy Water – 10

  • Bleach – 12

Along with these liquids and substances, many foods we eat contain an acidic pH because of their bacteria killing functions.

Understanding pH monitoring in Water

Now that you are familiar with pH basics, you may be wondering what it means for water quality. In truth, pH monitoring in water is critical because it helps determine the safety of water. Essentially, the pH value can inform us of whether water is hard or soft or even pure water, which has a pH value of 7. If water has a pH value lower than 7 it is acidic and higher than 7 it is basic. Normal values of pH in surface water systems range from 6.5 to 8.5 and 6 to 8.5 in groundwater systems.

Alkalinity is the measure of the capacity of the water to resist a change in pH that would tend to make the water more acidic. In order to determine the corrosiveness of water, you need to measure alkalinity and pH.

Generally, water with a pH level less than 6.5 could be acidic, soft, and corrosive. Water that is acidic could possibly contain metal ions like iron, copper, lead, zinc, or manganese, among other things. So if the water quality is acidic according to the pH scale, it contains higher than normal levels of toxic metals and can cause damage to metal piping or have associated aesthetic problems like a metal or sour taste. Additionally, it can cause laundry and sinks and drains to stain a blue-green color. However, most importantly, this kind of water is dangerous as it causes health hazards that go along with these toxins.

In order to treat water with a low pH level, use a neutralizer, which can feed a solution into the water to prevent it from reacting with household plumbing or from contributing to electrolytic corrosion. An example of a typical neutralizer is soda ash, or sodium carbonate, which works to raise the sodium content and in turn increases the pH.

If the pH level of water is higher than 8.5 this means the water could be hard, which does not necessarily pose a health risk, but can cause other problems like an alkali or bitter taste to water; a formation of scale deposits on dishes, utensils, and laundry basins; a hard time getting soaps to lather; and a formation of insoluble precipitate on clothes.

While a normal pH level of drinking water should be between 6-8.5, as humans, our bodies maintain pH equilibrium constantly and will not be affected by water consumption. As an example, our stomachs have a naturally low pH level of 2, which is a beneficial acidity that helps us with food digestion.


Resources: Free Drinking Water

Analytical Technology, Inc. designs, manufactures, and distributes analytical instruments based on electrochemical and opticcal sensors. ATI specializes in water quality monitors used in water treatment facilities including pH monitors such as the Q46P/R pH/ ORP monitor and the Q45P/R pH/ ORP transmitter.

Posted by: Caitlin Rickard

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