How to explain the movement of water from the roots to leaves?

Transpiration pull and root pressure moves water. Xylem sap ascends by solar-powered bulk flow.

The roots take up water by having more concentrated solutes (lower water potential) than the soil around the root with its high water potential. Charged ions like NH4+ & PO4- are assisted by facilitated transport to create a  one way gradient to draw water into the vascular cylinder. The roots actively create the osmotic gradient and a root pressure. http://plantphys.info/plant_physiology/transpire.shtml

Water molecules cling together or cohere and adhere to the xylem tissue. Like molecules cohere (cohesive whole) while different molecules adhere (different types of matter adhere to each other).

http://plantphys.info/plant_physiology/transpire.html
Transpiration and properties of water
http://generalhorticulture.tamu.edu/lectsupl/Water/water.html
Animation of water & sucrose movement in xylem & phloem
http://academic.kellogg.cc.mi.us/herbrandsonc/bio111/animations/0032.swf
Capillary action
http://www.uni.edu/~iowawet/H2OProperties.html