This calculator can be used to adjust the chlorine concentration of water to disinfect it for drinking and also for other applications. Typical levels of free chlorine (or residual chlorine) in drinking water are 0.2 - 2.0 mg/L though levels can be as high as 5 mg/L. Chlorine that is added to water is consumed first to become combined chlorine before it can emerge as free chlorine. Total chlorine is the sum of free chlorine and combined chlorine. There are test kits out there that test for free chlorine and total chlorine levels. Your initial chlorine addition may not give the free chlorine level that you expect because some or all of the initial chlorine added may be consumed to become combined chlorine. Please check literature on the internet that talk about water chlorination. For this application, concentration in ppm (parts per million) and mg/L can be used interchangeably. Available chlorine is the measure (expressed in percent by weight) of the amount of chlorine in the chemical used for adjustment. Common commercial chemicals used for water chlorination are water solutions of sodium hypochlorite and solid calcium hypochlorite. Household bleach (sodium hypochlorite solution) has 5% available chlorine content. Some calcium hypochlorite granules have 65% available chlorine content. Please check the label of container for available chlorine content or contact the manufacturer.