Radial-flow adsorption and ion exchange beds are considered for commercial water treatment processes on occasion, particularly for specialty applications such as nuclear reactor water cleanup. They have significant theoretical potential but some practical flow issues like short circuiting. For more common axial beds, at ultralow concentrations, a key design and operational performance factor is the mass transfer coefficient (MTC) that can accurately reflect the capabilities of the bed. MTC may be used as part of initial design but is most commonly used to monitor the status of fouling within the column. The question of whether MTC has the same meaning for both radial- and axial-flow is addressed. An analysis for ion exchange indicates that the method is still valid for MTC resin monitoring, and easily adapted to adsorption.