Drainage from the root zone of snap beans grown on a sandy soil was measured by a lysimeter, and calculated from Darcy's law, and by a hydrologic balance equation. At the end of a 60‐day period the Darcy's law calculation gave a 11% higher estimate of the cumulative drainage than the other two methods. Of the 32 cm of precipitation and decrease of 3 cm in water storage from emergence to harvest, evapotranspiration accounted for 17 cm, and drainage for 18 cm. A useful estimate of the drainage from the root zone in sandy soil was obtained from the space averaged capillary conductivity of the soil in which rooting occurred.