The system for determining chlorine demand in water includes a reagent supply tank configured for holding a solution of sodium hypochlorite of known concentration, a buffer tank positioned in fluid communication with the reagent supply tank, the buffer tank including a first conduit configured for transferring the solution from the reagent supply tank into the buffer tank, and a mixing tank positioned in fluid communication with the buffer tank, the mixing tank including a second conduit configured for transferring the solution from the buffer tank into the mixing tank to form a composite solution. The system further includes a first chlorine measuring device for measuring the free chlorine residual in a water source connected to the mixing tank, a second chlorine measuring device configured for measuring the free chlorine residual in the composite solution, and a pump operatively coupled to the water source.