Method of Operating a Capacitive Deionization Cell Using a Relatively Slow Discharge Flow Rate

1 . A method for efficiently softening water comprising:

(a) Assembling a cell comprising a cathode current collector, a first electrode capable of absorbing ions, a cation selective membrane, a spacer, an ion selective membrane, a second electrode capable of adsorbing ions, and an anode current collector;

(b) Collecting of a stream of clean water at a flow rate of F 1 , while applying a charge voltage of between about 0.5V and about 1.3V between said cathode current collector and said anode current collector for a first period of time, T 1

(c) Collecting a stream of waste water at a second flow rate, F 2 , while applying a discharge voltage between about −1.3 and about −0.5 V between said cathode current collector and said anode current collector for a second period of time, T 2 , such that

T 2 is greater than or about equal to 1−[T 1 *F 1 /(T 1 *F 1 +T 2 *F 2 )]*[T 1 +T 2 ] and T 1 *F 1 /(T 1 *F 1 +T 2 *F 2 ) is greater than or equal to about 0.7.