Water Supply in many parts of the world is a significant issue. Many regions face insufficient water for drinking, irrigation and other usages. When it comes to water usage, a significant amount of water is consumed by Irrigation relative to drinking water consumption. Supplying water for agricultural usage in arid and semi-arid regions is vital and challenging for agriculture. Treated wastewater is a suitable alternative for irrigation. The water has some chemical nutrients necessary for plant growth. Using treated Wastewater or treated polluted water has become as a part of the water supply management in many parts of the world. This book describes the use of treated wastewater for Irrigation. First, we state the effects of wastewater reuse in public health, plants and animals. Second, some of the existing standards and guidelines of treated wastewater for irrigation are reviewed. Third, a few methods of polluted water treatment are explained. Finally, surface water quality in the city of Tehran for irrigation usage is discussed.