BACKGROUND: This work evaluates hollow fiber liquid-liquid membrane contactors (HFMC) as a polishing step for the removal of low levels of ammonium from water purified by (or being supplied to) a membrane distillation unit in order to fulfil the conductivity requirements of hydrogen production by water electrolysis. RESULTS: The influence of the operating conditions (flow, pH, ammonium concentration, buffer capacity) were evaluated under a closed-loop setup in order to achieve a reduction of total ammonia concentration in water, from 15 to 1 mg L-1 to assure the production of water in the membrane distillation with a conductivity lower than 1 mu S cm(-1). These values were used to validate a numerical algorithm describing the system performance. In order to reach the ammonia concentration requirements and considering the low concentration of bicarbonate (low pH buffer capacity) in the treated water a buffer agent was added to the working solution. CONCLUSIONS: HFMC technology is a suitable solution to remove low levels of ammonium from water to values as low as 1mgL(-1)NH(3) through appropriate control of pH. The ammonium removal efficiency of the HFMC was improved by raising the pH or the flow rate. Finally, the model proposed provides a good description of the membrane contactor performance with minimal deviations when compared with experimental results. (C) 2016 Society of Chemical Industry