A dialysis system comprising: a dialyzer comprising a blood flow path, a dialysate flow path, a dialysate inlet for receiving fresh or regenerated dialysate into the dialyzer, and a dialysate outlet for discharging spent (used) dialysate from the dialyzer; a sorbent cartridge configured for regenerating spent dialysate, the sorbent cartridge comprising a sorbent cartridge inlet and a sorbent cartridge outlet; a fluid circuit comprising a first fluid passageway configured to provide fluid communication between the dialysate outlet of the dialyzer and the sorbent cartridge inlet, and a second fluid passageway configured to provide fluid communication between the sorbent cartridge outlet and the dialysate inlet of the dialyzer; a source of bicarbonate solution which is fluidly coupled to the second fluid passageway; a pump or orifice flow controller for delivery of the bicarbonate solution at a controlled rate from the source of bicarbonate solution into the second fluid passageway; and a supply of sterile water which is fluidly coupled to the second fluid passageway for introducing sterile water into the second fluid passageway from the supply of sterile water; wherein the dialysis system is adapted to: a) pass spent dialysate received from the dialyzer through the sorbent cartridge to produce regenerated dialysate that is discharged from the sorbent cartridge for circulation back to the dialyzer; b) introduce bicarbonate solution into the regenerated dialysate only during a first dialysis treatment time period to provide a treated regenerated dialysate that is circulated to the dialyzer; c) add sterile water to the regenerated dialysate during a second dialysis treatment time period occurring after the first dialysis treatment time period to provide a diluted regenerated dialysate that is circulated to the dialyzer; characterised in that the first dialysis treatment time period occurs within an initial 50% of total dialysis treatment time of a dialysis treatment session, and the second dialysis treatment time period occurs within a final 50% of the total dialysis treatment time of the same dialysis treatment session. a dialyzer comprising a blood flow path, a dialysate flow path, a dialysate inlet for receiving fresh or regenerated dialysate into the dialyzer, and a dialysate outlet for discharging spent (used) dialysate from the dialyzer; a sorbent cartridge configured for regenerating spent dialysate, the sorbent cartridge comprising a sorbent cartridge inlet and a sorbent cartridge outlet; a fluid circuit comprising a first fluid passageway configured to provide fluid communication between the dialysate outlet of the dialyzer and the sorbent cartridge inlet, and a second fluid passageway configured to provide fluid communication between the sorbent cartridge outlet and the dialysate inlet of the dialyzer; a source of bicarbonate solution which is fluidly coupled to the second fluid passageway; a pump or orifice flow controller for delivery of the bicarbonate solution at a controlled rate from the source of bicarbonate solution into the second fluid passageway; and a supply of sterile water which is fluidly coupled to the second fluid passageway for introducing sterile water into the second fluid passageway from the supply of sterile water; a) pass spent dialysate received from the dialyzer through the sorbent cartridge to produce regenerated dialysate that is discharged from the sorbent cartridge for circulation back to the dialyzer; b) introduce bicarbonate solution into the regenerated dialysate only during a first dialysis treatment time period to provide a treated regenerated dialysate that is circulated to the dialyzer; c) add sterile water to the regenerated dialysate during a second dialysis treatment time period occurring after the first dialysis treatment time period to provide a diluted regenerated dialysate that is circulated to the dialyzer;