Examine the animation above and consider the osmotic gradient between the lumen and the intercellular space (inside the villus). As sodium (green balls) is rapidly pumped out of the cell, it achieves very high concentration in the narrow space between enterocytes. The osmotic gradient is thus formed across apical cell membranes and their connecting junctional complexes. The arrow that appears denotes movement of water across the epithelium.
Water is thus absorbed into the intercellular space by diffusion down an osmotic gradient. However, looking at the process as a whole, transport of water from lumen to blood is often against an osmotic gradient - this is important because it means that the intestine can absorb water into blood even when the osmolarity in the lumen is higher than osmolarity of blood.
This ability is best explained by the "three compartment model" for absorption of water and, like many aspects of gut permeability, varies along the length of the gut. The proximal small intestine functions as a highly permeable mixing segment, and absorption of water is basically isotonic. That is, water is not absorbed until the ingesta has been diluted out to just above the osmolarity of blood. The ileum and especially the colon are able to absorb water against an osmotic gradient of several hundred milliosmols.