Most current models of the water uptake by plant roots from the soil profile solve the equation for flow of water in unsaturated soils. The boundary condition at the root-soil interface is represented, whether explicitly or implicitly by some kind of root distribution function. Such models have sufficient number of parameters so that they can be fitted to data reasonably well. Most water uptake patterns, when normalized with respect to root zone depth and plant extractable water reveal, remarkable similarities regardless of soil texture, plant species, or root distribution. This similarity is not predictable with current models. A model based upon non-linear behavior of the root membranes and described by a distributed sink moving downward through the soil profile adequately represents the uptake process. The shape of the sink function is not critical and only two parameters, a root depth parameter, and an extractable water parameter are needed.