Seepage testing using Fluoride
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Seepage testing using Fluoride

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Tracing Leaks using Fluoride

The fluoridation of public water supplies has always been a topic of debate with a small, mobile and very vocal group of people challenging councils all around New Zealand. Some areas stopped fluoridating their water supplies after these challenges and in April 2016, legislative changes were implemented allowing district health boards to direct local authorities to fluoridate community water supplies in their areas.

This change may see more or less water supplies fluoridated, but for those that still have fluoride there is another use it can be put to – finding leaks!

Councils and other organisations have active leak detection procedures in place, but vast quantities of water is still lost each year. This lost water can also cause problems as it erodes hillsides, creates sinkholes, floods basements and destroys property.

Eurofins-ELS can test water samples taken from areas of suspected leaks for fluoride – we call these Seepage samples.

Fluoride is a remarkably good tracer because it stays in the water even if it has flowed for long distances or through soil and retaining walls. If the test sample returns a similar level of fluoride to a tap water sample then it can be assumed the leak is from a water pipe.



A suite of tests is offered by Eurofins-ELS to identify if a leak is one of four different sources: PotableSewage, Seawater or natural groundwater/rainwater. Comparing the results of the tests to the following table gives a likely source.

However there are some factors that may affect the outcome of the tests.

  • The water supply must be fluoridated – not all supplies are, and some are intermittent
  • Natural fluoride level in NZ groundwater is usually below 0.2 g/m3 but this can differ between regions
  • Rainwater may have diluted the test sample
  • Sunlight may have concentrated natural groundwater fluoride through evaporation
  • Seawater may also affect the reading because it contains a high level of fluoride
  • Fertiliser contains fluoride as well, so the test sample may have absorbed extra fluoride

If you have discovered a leak and would like a sample tested please contact us