Water from soil enters into the root hairs owing to :

In plants, the transpiration stream is the uninterrupted stream of water, and other, which is taken up by the roots and, via the xylem vessels, transported to the leaves where it will eventually evaporate into the air/apoplast-interface of the substomatal cavity. It is driven in by capillary action and in some plants root pressure. The main driving factor is the difference in water potential between the soil and the substomatal cavity caused by transpiration.