A flow loop for hemodialysis, hemodiafiltration and hemofiltration for the treatment of pathological conditions such as End Stage Renal Disease (ESRD) that has a controlled compliant flow path for preparing fluids required for a hemodialysis therapy session from water. The controlled compliant flow path modifies water into any one of a solution for priming a hemodialysis system, a physiologically compatible solution for contacting blood, a physiologically compatible solution for infusion to a subject, and a solution for blood rinse back to a subject. The controlled compliant flow path has a means for selectively metering in and metering out fluid from the flow path.