Dialysis systems including a water treatment unit preferably of the osmosis type, a drain line, and a heat exchanger are disclosed. A water supply line is connected to an outlet of the water treatment unit. The water supply line includes branch connections to which dialyzers are selectively fluid-coupled. Used-up dialysis fluid can be discharged from fluid-coupled dialyzers through the drain line. The heat exchanger, which is external to the dialyzers, connected on one side to the water supply line directly upstream of the branch connections and on the other side to the drain line.
