Streaming potential study showed that the water transference coefficients of Nafion 117 equilibrated with solutions of aliphatic ammonium chlorides which have both hydrophilic and hydrophobic parts increased with the increase in the size of aliphatic ammonium cations, which was definitely opposite to the trends observed in the case of alkali and alkaline earth metal cations. The result revealed the fact that the pumping effect of the cations indeed exists and would be the dominant contribution in the case of hydrophobic cations. In the case of hydrophilic cations, cations together with strongly hydrated water molecules pump loosely-bound or peripheral water molecules.