Water reuse is no longer a choice, it’s an essentiality. Sewage is considered as one of the stable and significant sources of alternative water. Limitation of water resources and fluctuations and climate changes, uneven distribution of water in the world, increasing population, pollution of surface and underground water, and reaching the stage of water stress in many countries made water managers and planners seek to use non-conventional sources of water to achieve sustainable development. Therefore, the use of wastewater as a reliable source of water in terms of quantity in various sectors, including agriculture and industry, has received serious attention. In line with the optimal management of water resources and achieving the desired situation and providing water needs in the future, measures such as demand management and increasing social awareness, supply management, prioritizing consumption, using returned water, increasing water productivity, etc., it is essential. One of the important solutions in this field is the recycling and reuse of wastewater, which leads to the reduction of surface and underground water consumption. The use of treated wastewater has many advantages, including a higher availability of water, sustainable utilization of water resources, reduced energy consumption, decreased nutrient loads, and increased production. It also promotes environmental protection and boosts employment and the local economy. The advantages of reusing wastewater will be discussed in this chapter.