A system for purifying incoming fluid is provided that is modular and includes a heat exchanger module, an evaporator-condenser module and a compressor. The system is configured to facilitate passivedrainage of the purified fluid for collection. The system components are arranged in a stacked configuration to facilitate gravitational flow of the purified fluid such that the purified fluid drainspassively for collection. A system for preparation of ready-to-use treatment fluid is also provided including the modular fluid purification system, a preparation station and a coupling device. The components are configured to be retained in a portable carrier that is manually operable for improved access to and mobility of the components. A coupling device for use in connecting flow channels of aplurality of components and for use in preparing ready-to-use dialysate is also provided, a further system for preparation of a receptacle and a ready-to-use treatment fluid in the receptacle is provided.