In arid and semi-arid regions, as most of the Mediterranean countries, the use of unconventional water resources has been seen to play an ever more important role in satisfaying the increasing water requirements. It is quite difficult to make a classification of the unconventional water resources. Water quality is the most important factor in managing unconventional water resources: quality is a complex factor since there are many water quality parameters which vary with continuity. Two major categories of unconventional water resources could be identified, the first including waters with high organic matter and microorganism content (such as municipal wastewater) and the second including waters with high saline concentration (such as sea and brachisk water, some industrial and agricultural wastewater, etc.). In many Mediterranean countries municipal wastewater reuse has been practiced for a long time and actually represents the most relevant use of unconventional resources. In this paper a network is presented which highlights the main indirect effects of the agricultural use of municipal wastewater. The resources of research and the anlysis of case studies lead as to the conclusion that the development of irrigation with wastewaters may have a certain importance in the Mediterranean countries. There are good reason for up specific and realistic regulation, which would be based on the recent whole guidelines.