Tehran Province Water and Wastewater Company is in charge of clean water supply as well as the hygienic disposal of sewage of the urban districts of Tehran Province. Having an area of 18,900 km2 (1.2 percent of the total area of the country), Tehran accommodates about 20 percent (14 million people) of the total population of Iran. At the same time with 92 percent of urban population in 13 cities and 54 towns, Tehran Province enjoys the highest level of urban dwelling in the country and 44 percent of the industry of the country is in this province.TPWW Company and its sub-companies are in charge of supplying urban water as well as establishment of other installations related to the collection, disposal and treatment of wastewater as well as their management in the cities of Tehran Province. Indeed TPWWC functions as headquarter, policymaking body and umbrella structure for the eight executive companies in Tehran Province having 5150 permanent and 2600 temporary staff. Yearly precipitation average in Tehran province is 230mm and the renewable water resources rate is approximately 4.2 billion m3/year that regarding the high rate of population in the province it creates a low rate of renewable resources per capita. According to the world standards the renewable water recourses per capita below 500m3/year is indicative of absolute water crisis in the middle east.