Israel has declared war against drought. Five desalination plants generate around 600 million cubic metres of fresh water every year, which is about 70 percent of the consumption required by private households. Because the vast plants cannot be regulated flexibly, in times of lower demand and when the supply lines are being worked on, the country has too much of the precious wet stuff. "They need intermediate storage capacity," says Prof. Dr. Christoph Schüth, Professor of Hydrogeology at the TU Darmstadt. The water is fed into porous layers in the subsurface known as aquifers, and stays there until it is needed. This has one disadvantage: the desalinated water is chlorinated. If it seeps through the soil, the chlorine reacts with organic substances in the soil and toxic compounds such as chloroform are formed.
In the German-Israeli joint project "MAR-DSW", Schüth, Dr. Kaori Sakaguchi-Söder and doctoral candidate Behane Abrha want to find out what happens to these trihalomethanes in the water. They do this using stable isotope analysis, a method which Sakaguchi-Söder has developed further in her doctoral thesis and customised for the analyses in Israel. "This method is a speciality of the TU, and it enables us to establish the isotopic composition of all elements that form the trihalomethanes," she explains. Water samples are taken from various points of the aquifer and analyzed in a gas chromatograph that "blows up" the molecules in it.