The Hi701 Checker HC (Handheld Colorimeter) is a simple, accurate and cost effective way to measure free chlorine. Free chlorine is the active form of chlorine used for disinfection of drinking water, swimming pools and spas, and vegetable rinse water. Free chlorine in water is also harmful to a reverse osmosis membrane and needs to be monitored for removal from source water prior to being used. Designed as a more accurate alternative to chemical test kits, the Hi701 free chlorine meter provides quick, accurate results in a few easy steps