Water treatment systems, devices, and methods for fluid preparation

A method of delivering a blood treatment, comprising:

• carbon-filtering primary tap water to generate chloramine-free water;
• deionizing the chloramine-free water to a predetermined level of resistivity, to generate deionized product water, the predetermined level being selected to be low enough to permit a detection of chloramine in the deionized product water resulting from a failure of said carbon-filtering;
• using a controller determining that at least one carbon filter used to perform said carbon-filtering is to be replaced and, responsively to said determining, outputting an alarm signal to replace said at least one carbon filter;
• said determining being effective to ensure that a chloramine level in said deionized product water is below a predetermined safe level for use in a dialysis, hemodiafiltration, or hemofiltration treatment of a human, said predetermined safe level being according to a predefined medical standard with a margin for safety based on a predicted water quality and a predicted chloramine removing efficacy of said at least one carbon filter;
• ensuring in an event an error in said carbon-filtering, that said deionized product water is safe, detecting chloramine in the deionized product water resulting from a failure of said carbon-filtering and controlling a flow of said deionized product water responsively thereto;
• wherein said detecting includes converting a resistivity signal to a chloramine level based on data representing a relationship between chloramine level and resistivity stored in the controller.