Abstract:This study was conducted to determine the efflux of specific ions, including fluoride, from a deionization (DI) water purification system (WPS) when the WPS was operated beyond exhaustion of the DI resin. Effluent from the DI WPS was monitored for resistivity, total dissolved solids, pH, and concentrations of silica, fluoride, potassium, and sodium. After 16,000 L of water was purified, the resistivity declined to 0.492 Ω Ohm‐cm, and silica was released from the DI WPS. Fluoride ions were released after an additional 8,000 L water was treated, and the resistivity fell to 0.07 Ω Ohm‐cm. The fluoride efflux reached a peak of 32 mg/L, 28 times greater than the original fluoride concentration in the city water. Sodium and potassium ions were released after approximately 26,000 and 32,000 L of water had been treated and reached peaks of 76 and 47 mg/L, respectively. This study confirms that the minimum resistivity standard of 1 Ω Ohm‐cm for DI water used for hemodialysis should provide an adequate safety margin. Once resistivity fell to 1 Ω Ohm‐cm, more than 8,000 L of water was treated before fluoride efflux occurred. Accordingly, hemodialysis centers should be attentive to the calculated capacity of their DI WPS and reliably monitor the resistivity to prevent patient illness related to exhaustion o
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