Systems and methods for using a sodium chloride source and a buffer source such as sodium bicarbonate in a controlled compliant flow path to generate from water a physiologically compatible fluid having a suitable level of a sodium ion and/or a buffer for use in hemodialysis, hemodiafiltration and hemofiltration. The system has a conditioning flow path that has at least a salination valve or salination pump, and at least one container has at least one solute in excess of the solubility of that solute. At least one of the solutes is a buffer source or sodium chloride. The conditioning flow path is in fluid communication with a controlled compliant flow path. The conditioning flow path can selectively meter fluid into and out of the controlled compliant flow path.