A water preparation apparatus for determining an amount of total chlorine in purified water is disclosed. The water preparation apparatus includes a chlorine sensing system, a water pretreatment filter, a reverse osmosis filter, and an electrodeionization (“EDI”) module. The chlorine sensing system is configured to determine an amount of total chlorine in the purified water by applying, at a first time, a source voltage to the purified water and removing, at a second time, the source voltage. The chlorine sensing system then measures, after the second time, an electrical parameter of the purified water. The chlorine sensing system determines the amount of total chlorine in the purified water based on the measured electrical parameter.