Fluoride Measurement in Drinking Water

Fluoride in Drinking Water

The use of fluoride as an additive to drinking water has been a highly debated topic for over 70 years. Although fluoride occurs naturally in many water sources, it is often added to water supply systems to provide health benefits to the public.  While the positive effects of fluoride on dental health have been scientifically proven, many citizens are concerned about the effects of fluoridated water on their health and believe that fluoridation is a freedom of choice issue.

The history of fluoridating water dates back to the early 1900s when Dr. Frederick McKay, a young dentist from Colorado, USA, observed many of his patients from the Pikes Peak region displaying stained and pitted teeth, known as fluorosis. However, he noticed that these patients had fewer cavities than many of his other patients. Scientists originally believed the cause was calcium related. After decades of research, it was concluded that runoff water from the Pikes Peak rock formations contained high amounts of fluorine minerals that raised fluoride levels in the region’s water supply.

As more research was conducted and published, word spread about the health benefits of fluoride when administered at proper dosages. By the 1950s, pilot programs were introduced to measure the health benefits of artificial fluoridation on drinking water.

These test programs were highly successful in preventing tooth decay, leading to widespread acceptance of artificial fluoridation. Australia is one of the countries that have water fluoridation programs currently operating. The acceptance of the benefits of water fluoridation occurred in Australia in December 1953, roughly two years after acceptance in the United States. Now, artificially fluoridated drinking water is provided for 70% or more of the population in all states and territories. Water fluoridation is an effective, inexpensive and socially equal way to reduce tooth decay in children and adults.

The addition of fluoride to a drinking water supply is generally governed by the Australian Drinking Water Guidelines. The Guidelines recommend a health-related guideline value (maximum concentration) of 1.5 mg/L for fluoride, which mirrors the World Health Organisation Guidelines for Drinking Water Quality. The use of fluoride is also controlled by state and territory legislation and regulations, as well as local regulations: in some areas, fluoride occurs naturally in drinking water.

Fluoridation is generally achieved by adding either a slurry of sodium fluorosilicate, a solution of hydrofluorosilicic acid or (less commonly) a saturated solution of sodium fluoride, added as a metered dose for a given rate of water flow. Correction of pH may be needed out after fluoride addition.

To ensure the level of fluoride lays within the recommended limits, the Australian Drinking Water Guidelines recommend measuring fluoride concentration in drinking water using an ion-specific electrode (APHA Method 4500-F- Part C 1992).



A drinking water treatment plant contacted Hanna Instruments for a way to measure fluoride in their source water and finished drinking water. By testing fluoride concentration in their source water, the treatment plant could adjust their fluoride addition and ensure compliance with the permit limit of 1.5 mg/L.  Hanna Instruments suggested the HI5222 Benchtop Research Grade pH/ORP/ISE Meter with the HI4010 Fluoride Half Cell Ion Selective Electrode and the HI5315 Reference Electrode for ISE Half-Cells.

Hanna Instruments suggested that the customer use the “known addition” incremental method feature built into the HI5222 for measurement of fluoride at low concentrations. In this method, the user performs a sample reading both before and after adding a standard of known concentration to the sample. The HI5222 provides built-in prompts and formulas for multiple incremental methods to guide the user through the procedure without having to perform manual calculations. The customer appreciated the ease of use in taking measurements as well as the increased accuracy and repeatability of the known addition method. The 100,000 data point capacity (per channel) enabled them to store and recall large amounts of data without worrying about exceeding memory limits. Overall, the customer valued the accuracy and ease of testing fluoride levels using the HI5222 and fluoride ISE.


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