Climate change affects water resources worldwide, and Southern Europe is one of the areas where water scarcity is expected to increase in the future. Different water scarcity indicators discussed in this manuscript (e.g. total annual actual renewable water resources, water exploitation index and dependency ratio) showed that some parts of this region are already facing water stress and that climate change could have a great impact on their water supply sector. As agriculture is the biggest consumer of water in the world and also in this particular region, potential water scarcity will impose the need to find new water sources. Treated wastewater reuse would decrease the pressure on the environment and is especially suitable for reuse in agriculture since it already contains some nutrients required for plant growth. However, in order to use it safely, treated wastewater must reach a certain quality that should be regulated. In the south of Europe, 4 countries out of 15 have already adopted wastewater reuse regulations (Greece, Italy, Portugal and Spain). This review compares these regulations and discusses their differences.