In each of the groundwater projects more than 14 laboratories from ten countries participated. In the study, each laboratory uses its own measurement technique to determine levels of chemicals in a common water sample. This gives the analysts a chance to see how well their method performs against others. It also provides a forum for discussing the results and, more importantly, the reasons for varying results. The participants pick up new skills and ideas from this technical meeting.
Specialised laboratories prepare reference materials.
They start with an enormous sample of water that has been contaminated, up to 200 litres. For instance, the Danish Geological Survey knew where to find natural groundwater supplies with quite high levels of bromide. Sometimes, natural supplies cannot be used because of dissolved organic material that changes the water's composition over time or disrupts measurement of certain substances. In these instances, artificially prepared groundwater is used. The groundwater is divided up into about 1,000 samples.