Tigernut (Cyperus esculentus L.) is an herbaceous oil crop uniquely accumulating a high level of oil in the underground tubers. Water, which accounts for approximately 85% of immature tubers, is essential for tuber development and metabolism. Plasma membrane intrinsic proteins (PIPs) represent the main channel that mediates the efficient water transport across the cell membrane. This study presents the characterization of CePIP2;1, a PIP gene highly abundant in tigernut tubers. This gene with three introns was shown to encode 288 amino acids with the theoretical molecular weight of 30.34 kDa, the isoelectric point of 8.60, the grand average of hydropathicity of 0.529, and the instability index of 29.60, implying it’s stable, basic and hydrophobic characteristics. The protein was shown to possess one conservative MIP (major intrinsic protein) domain, and presence of the F-H-T-R ar/R selectivity filter and Q-S-A-F-W Froger’s positions implies a putatively efficient water transport activity. Phylogenetic analysis revealed that CePIP2;1 clusters with OsPIP2;1, OsPIP2;2, and OsPIP2;3 with the similarities of 91.72%, 90.31% and 84.98%, respectively, supporting its assignment into the PIP2 group of the PIP subfamily. Subcellular localization analysis showed that CePIP2;1 was localized to the cell membrane of Nicotiana benthamiana leaves. Although CePIP2;1 was characterized as a dominant isoform in tubers, expression analysis indicated that its transcripts were relatively more in leaves, leaf sheaths, rhizomes, and roots with the most in leaves, in contrast to a comparable level to that in shoot apexes. Among four typical stages (S₁–S₄) of tuber development examined in this study, CePIP2;1 was shown to exhibit a bell-shaped expression pattern, peaking at S₂. These results laid a solid foundation for further uncovering the mechanism of water balance in tigernut.