The device (100) has a fluid container (15) for accommodating fluid i.e. reverse osmosis water, and a concentrate retainer (3) for accommodating concentrate. A concentrate connection is provided for addition of another container containing the concentrate and a preparation unit. The preparation unit is arranged and designed in such a manner that the fluid from the fluid container is mixed with the concentrate from the retainer and/or from the latter container containing the concentrate, in the preparation unit. An independent claim is also included for a method for filling a dialysis machine with a dialysis fluid and for discharging the dialysis fluid from the dialysis machine.
