Of all the chemicals produced in the world today, only a fraction have been studied for their possible harmful effects. Also, each year more new chemicals are produced, although their effects may not be understood. EPA has studied only the more common chemicals, especially pesticides and herbicides, mainly concentrating on whether they cause cancer or birth defects. A great deal remains unknown. Some of the wastewater from the Roger Road Treatment Plant receives tertiary treatment in a City of Tucson facility and distributed for use on golf courses and other turf facilities.
Tertiary treatment involves treatment through sand filters or soil and additional disinfection.
Part of the effluent is taken to Sweetwater Wetlands, an artificial wetland Tucson Water completed in 1998. This wetland adds another layer of treatment before discharging the water to recharge basins. Artificial wetlands have become increasingly popular in Arizona in recent years as they serve not only to treat the water, but also provide wildlife habitat and recreation. A small amount of wastewater is taken from the Ina Road plant for agricultural use and to irrigate the county's Arthur Pack Golf Course. Some areas, such as Green Valley, are located far from major treatment plants and have their own small facilities, almost all of which are operated by Pima County.