Chlorine is the most widely used disinfectant for drinking water and is also important for sanitizing swimming pools, cooling towers, other industrial equipment and treatment of wastewater. Its measurement and control are vital for both safety and economic reasons. Many Hach chlorine tests have been accepted by the U.S. Environmental Protection Agency for reporting purposes. Test kits containing DPD colorimetric reagents are used most often for monitoring potable water, swimming pools and waste effluent. Kits for determining higher levels of chlorine use thiosulfate to measure chlorine titrimetrically.