A method of preparing a dialysate solution for hemodialysis, the method including the steps of providing a mixing pump comprising a pump chamber covered by an actuable membrane, the chamber having a first inlet for admitting water into the chamber, a second inlet for admitting dialysate base solution into the chamber, and an outlet from the chamber, the method including the further steps of providing pump means for dispensing a predetermined volume of dialysate solution base into the chamber at a first pressure, actuating the membrane to draw a volume of water or water mix into the mixing pump chamber at a second pressure, wherein the magnitude of the first pressure is higher than the magnitude of the second pressure so as to ensure the complete dispense of the dialysate solution base into the chamber.
