The further from the tip, the less water that is taken up by the root. This roughly correlates to the region of the roots that is suberized. However, it must enter the stele symplast because of the Casparian strip . Root as osmometer Analogy - allows for the development of root pressures in the stem. These can be measured and are about 0.2 - 0.3 MPa.
Evidence comes from various tracer studies where xylem is loaded with dyes.
I'll bet you've done the classic celery stalk in food coloring experiment. The primary water transport cells are tracheids and vessels. Note that gymnosperms only have tracheids whereas angiosperms have both and primarily rely on vessels for water transport. Both tracheids and vessels have pits, thin circular regions, in the walls. According to Poiseuille's Law - flow rate is directly proportional to the pressure gradient and the cross sectional area of the pipe but inversely proportional to the viscosity of the fluid.