A low-flow equation is derived from Darcy's law and a mass balance equation for base flow from a hillside by assuming that groundwater recharge is constant over short time periods. This low-flow equation reduces to many of the existing mechanistic low-flow equations, but in its general form looks like a linear regression model and captures spatial variability in base flow among hillsides in a basin. As a result, it unifies the mechanics and statistics of low flows in river networks. This equation is tested against low-flow data from the Flint River basin in Georgia and the Gasconade River basin in Missouri, both of which are approximately 700 km2 in size. ¿ 2000 American Geophysical Union