Starting from flow equations in a 3D root architecture, we derived a general root water uptake equation with three characteristics root system properties: root system conductance, uptake distribution for uniform soil water potentials, and a compensatory uptake matrix. This equation can be scaled up straightforwardly and implemented in 1D soil water balance models and is a generalization of other models like the parallel root and big root models. We illustrate how the model can describe uptake by mixed vegetation.