The chlorine level in the water after the chlorine demand has been satisfied. The free available chlorine is the true measure of the chlorine disinfectant. The residual level is usually maintained by use of tablets, or a chlorine generator. Although a residual level can be maintained by daily additions of granular sanitizer, tablets (or sticks) are far more convenient and reliable for a consistent level of sanitizer, only exceeded by a chlorine / ozone generator.