Where did the Water Come From?

portrait photo of Richard

Richard T. Edwards, P.E.

As a materials engineer with some experience in chemistry, I am often asked to assist other engineers in determining the source of water in a crawlspace or an affected area. Obviously, seawater versus freshwater is not a difficult determination. This can be differentiated by simple turbidity tests or other methods. Turbidity just checks for the presence of chloride salts by visual cloudiness.

The most difficult distinction usually comes down to trying to discriminate between fresh surface water and tap water. Since many municipalities use surface water for their water supply, the differences can be minor and are limited to those modifications made by the city water plant. Sometimes, we are asked to discriminate between accumulation of condensation and tap water. Sample sizes are often limited to just a few milliliters so the number of tests is limited. Commercial water testing facilities will not attempt to test samples less than 16 ounces or 500 milliliters.

So, our “arsenal” of tests that can be run for validating or eliminating a source of moisture in a problem area is as follows:

  • Chlorine 
  • Fluoride
  • Conductivity
  • Sulfates
  • Nitrates
  • pH

I’ll try to explain each of these tests as to why we would use these particular analytical techniques...

  • Chlorine is a gas added to municipal water supplies for disinfection. Once water has been standing in open air for more than a day or so, it evaporates from the water sample. Therefore, using it as a discriminator on standing water is not a definitive test.
  • Fluoride is added to municipal water supplies for public health reasons and to minimize tooth decay. Most people believe that it doesn’t occur naturally, but in fact, there are areas all over the country that have mineral deposits of fluorspar. Fluorspar is a fluoride-containing mineral that can add fluoride to well water and subsurface water supplies with fluoride concentrations that are comparable to municipal water supplies. We test for fluoride using an ion-specific electrode and backcheck the area’ s geology for fluorspar to see if fluoride is a reliable discriminator.
  • Conductivity is a useful discriminator when discussions of a condensate accumulation are posed as a possible source of water. Condensate is, essentially, distilled water and therefore very pure with very low conductivity. Any other possible sources of water will have conductivity orders of magnitude larger than accumulated condensate (provided the condensate is not sitting on earth with soluble minerals).
  • Sulfates can be found in surface water runoff and tap water and other sources. If sulfate-containing fertilizers are used in the area, surface water concentrations of sulfates will be orders of magnitude higher than most other sources.
  • Nitrates, also a component of fertilizer, are tested in a similar fashion as sulfates and can be helpful in identifying surface water runoff into a crawlspace.
  • pH, the measure of a water sample’s acidity or alkalinity, can be useful if the values are deviant from neutral (~6.0-8.0). On its own, pH should not be used as a discriminator unless the values are extremely deviant. Other tests should always be run, when possible. pH can be tested using small handheld meters, laboratory bench-style meters, a pool testing kit, or special indicator paper strips. A pool testing kit can also test for free chlorine concentrations, as well as pH.

So, if you want to test the water in a structure to determine its source, try to think of the following rules:

Collect as much as you can, one liter or one quart if possible. Use clean containers and rinse them out, if possible, with the subject water source.

Collect samples from the possibilities. For example, one sample from the faucet, one sample from the puddle or water of interest, and a sample from any nearby potential source, such as a marsh or a golf course sprinkler.

Label the samples with the source information, date of collection, and a contact number for the collection personnel.

These rules are not hard and fast, we have done successful discrimination tests on samples of 2-3 mL (1/10 ounces). However, the smaller the sample, the more information we will need about the circumstances of the problem and the collection.

In short, testing for the source of water is not like a bad detective movie, where the victim exudes water from his lungs that smell like pool water. Chlorine does not persist long enough to make this a reliable test. (Although, chlorine is a useful test and should be used when possible)

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