A system for purifying incoming fluid is modular and includes a heat exchanger module, an evaporator-condenser module and a compressor. The system components are arranged in a stacked configuration to facilitate gravitational flow of the purified fluid such that the purified fluid drains passively for collection. A system for preparation of ready-to-use treatment fluid includes 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 can connect the flow channels of several components and can be used in preparing ready-to-use dialysate. A system prepares a receptacle and a ready-to-use treatment fluid in the receptacle.
