Areas of Work
Determining the origin of water-caused damage using the isotope method
The repair of water-induced damages requires knowledge of the specific cause. Especially in cases of water damage in buildings, the origin and the path of water is not always known. To determine the cause of a water damage, however, it is often sufficient to differentiate between tap water and precipitation. In these cases, the isotope method has proved to be an elegant and practical alternative to conventional leak detection methods.
Water is a mixture of common and rare hydrogen and oxygen isotopes. These isotope mixtures are subject to a constant change due to fractionation processes (evaporation and condensation) in the water cycle. Global measurements of precipitation have indicated an approximately stable linear relationship - known as the Global Meteoric Water Line.
In contrast, isotope signatures of regional tap waters, in most cases, are relatively constant. They lie mostly on or at least close to the Global Meteoric Water Line. This relatively constant isotope signature of tap water is used for determining the origin of a water damage. In order to identify the origin of a damage-causing water, the isotope signatures of tap water and the damage-causing water are usually compared to each other. Since damage-causing water, in most cases, underlies evaporation processes leading to changes in the isotope signature, a back projection to the original composition is required. Knowledge about the environmental conditions of the damage-causing water allows this process to be traced on an evaporation line. The comparison of the values of tap water and damage-causing water in many cases allow the desired distinction - and thus the determination of the origin of the damage-causing water.
Due to the different atomic weight, isotopes physically behave slightly differently. This leads, for example, to a change in the isotope ratios during phase changes (e.g. evaporation and condensation). For example, water molecules with light isotopes preferentially evaporate from a water body, while the "heavy" molecules accumulate in the remaining water body. These changes of the isotope ratios are called "isotope fractionation".
In general and for water in particular, isotope fractionation is temperature dependent. Therefore, the annual variation of air temperature in our latitudes results in an annual variation of isotope signatures in precipitation (Figure 1). Thus, precipitation in the cold winter months shows significantly more negative δ-values than in the warmer summer months.
Figure 1: Annual variation of oxygen-18 and deuterium values in precipitation in Schweitenkirchen, averaged from monthly values of the years 1999 - 2015.
The isotope ratios in precipitation also differ regionally due to temperature, altitude and origin of the precipitating air masses. If the isotopic ratios of oxygen and hydrogen of precipitation are plotted against each other in the so-called oxygen-18-deuterium diagram, the corresponding δ-values scatter in the range of a straight line, the mean global precipitation line (GMWL, Figure 2), despite the large variation of isotopic ratios of precipitation worldwide. The intercept of the GMWL of 10 (‰) is called the "deuterium excess" (d) (see formula in Figure 2). If the deuterium excess of a water sample deviates significantly from 10 ‰, i.e. if it is below or above the GMWL, this indicates phase changes in the water.
Figure 2: Oxygen-18 deuterium diagram. Also plotted is the GWML as well as value ranges of precipitation that fell under different conditions and the water reservoirs formed by this precipitation, as well as the typical change in isotopic signatures due to evaporation and condensation.
As a result of isotopic fractionation, water bodies such as groundwater and the tap water usually derived from it exhibit regionally varying δ-values.
The differences in isotopic signatures of waters resulting from the effects described above are used to evaluate the origin and modification of water.
For the isotope analyses of water, a sample volume of 2-4 ml, filled into glass- or PET-bottles, is sufficient.
The recovery of damage-caused water can be done from material samples as well. If it is not possible to obtain water samples directly, because the moisture is bound in components or building materials, we can provide the necessary equipment. For this purpose, prepared silica gel is filled into plastic tubes and sent to you in an airtight packaging.
These absorber tubes are then inserted into boreholes in the building material or the component – for example a masonry - and sealed airtight. After approximately 10-14 days, the silica gel has generally absorbed sufficient moisture so that the absorber tubes - again sealed airtight - can be sent to us to recover the absorbed water for the analysis.
