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Some plasma membrane intrinsic protein (PIP) aquaporins can facilitate ion transport. Here we report that one of the 12 barley PIPs (PIP1 and PIP2) tested, <i>HvPIP2;8</i>, facilitated cation transport when expressed in <i>Xenopus laevis</i> oocytes. <i>HvPIP2;8</i>-associated ion currents were detected with Na⁺ and K⁺, but not Cs⁺, Rb⁺, or Li⁺, and was inhibited by Ba²⁺, Ca²⁺, and Cd²⁺ and to a lesser extent Mg²⁺, which also interacted with Ca²⁺. Currents were reduced in the presence of K⁺, Cs⁺, Rb⁺, or Li⁺ relative to Na⁺ alone. Five HvPIP1 isoforms co-expressed with <i>HvPIP2;8</i> inhibited the ion conductance relative to <i>HvPIP2;8</i> alone but HvPIP1;3 and HvPIP1;4 with <i>HvPIP2;8</i> maintained the ion conductance at a lower level. <i>HvPIP2;8</i> water permeability was similar to that of a C-terminal phosphorylation mimic mutant <i>HvPIP2;8</i> S285D, but <i>HvPIP2;8</i> S285D showed a negative linear correlation between water permeability and ion conductance that was modified by a kinase inhibitor treatment. <i>HvPIP2;8</i> transcript abundance increased in barley shoot tissues following salt treatments in a salt-tolerant cultivar Haruna-Nijo, but not in salt-sensitive I743. There is potential for <i>HvPIP2;8</i> to be involved in barley salt-stress responses, and <i>HvPIP2;8</i> could facilitate both water and Na⁺/K⁺ transport activity, depending on the phosphorylation status.