Water travels from the soil to the root xylem through the apoplast (i.e., cell wall space) and/or cell-to-cell, but hydraulic barriers in the apoplast (e.g., suberized structures in the endodermis) can force water to traverse cell membranes at some points along this path. Anytime water crosses a cell membrane, its transport can be affected by the activ-ity of membrane-intrinsic water channel proteins (aquaporins). We review how aqua-porins can play an important role in affecting root water transport properties (hydraulic