Aim of the investigation was to clarify the origin of water leaking from a suspended ceiling on the upper floor of an office building.
To identify water bodies of different origins, the isotope analysis proved to be particularly suitable. By determining the relative proportions of the heavier water isotopes ²H and ¹⁸O in the sample water, these can be assigned to different sources. This makes it possible to distinguish between groundwater, rainwater and condensate water. Isotope analysis usually enables a clear distinction to be made between infiltrated rainwater and tap water.
The proportions of the heavier isotopes are determined in the so-called δ (delta) notation The measured isotope ratio RR relative to the isotope ratio of a standard, usually the Vienna Standard Mean Ocean Water (VSMOW), then 1 is subtracted and multiplied by 1000. The result is given in “‰ VSMOW”.
Worldwide, the delta values are scattered in a line that can be described as global mean precipitation line (GMWL) The intercept of this line is called deuterium excess (d) If the deuterium excess of a water sample deviates significantly from ±10 ‰ – i.e. is below or above the GMWL – this indicates phase changes such as Evaporation or condensation The degree of deviation from the GMWL depends on the humidity and temperature conditions during evaporation. The projection of such an altered sample onto its original isotopic composition is called evaporation or condensation line.
The analysis of the contaminated water sample showed that its values are significantly above the precipitation line. With an increased deuterium excess of 32 ‰ This sample shows typical changes due to condensation-induced isotope fractionation. This is clearly condensed water from the concrete ceiling.
And finally ... The water escaping from the suspended ceiling clearly comes from condensation processes and not from another body of water.
