The threat posed to drinking water resources by persistent and mobile substances has been recognized for decades. However, for many contaminants, some of which have been detected in drinking water resources for decades, there is still no conclusive assessment of their intrinsic biodegradability in the aquatic environment by the responsible companies. The recommendations are intended to make it easier for a wide range of users, such as water utility laboratories and government agencies with established analytical facilities, to perform a "cold" degradation test in accordance with OECD TG 309 for substances found in their own water resources.