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A study was conducted at 12 sites across the United States to evaluate field-scale hydrology of landfill final covers using water balance methods to control percolation. The sites were located in climates ranging from arid to humid, with annual precipitation varying from 119 to 1,263 mm. Fifteen test sections were constructed with large (10x20 m) drainage lysimeters for continuous and direct monitoring of the water balance over a period of 3-6 years. Monolithic and capillary barrier designs were used for water storage, and plant communities consisting of grasses, grasses and shrubs, or grasses and trees were used to promote evapotranspiration. Data from these test sections are analyzed along with data from 10 other sites in the literature to draw general inferences regarding the hydrology of water balance covers. Percolation ranges from 0 to 225mm/year (0-34% of precipitation) on an average annual basis and is shown to be affected by annual precipitation, preferential flow, and storage capacity of the cover. Evapotranspiration is the largest component of the water balance (>60% of precipitation) and varies with water availability from precipitation, energy demand as characterized by potential evapotranspiration, and type of plant community. Surface runoff is the smallest fraction (<16% of precipitation) and depends on the saturated hydraulic conductivity of the surface soils, intensity of precipitation, and the occurrence of snowmelt and frozen ground. (C) 2014 American Society of Civil Engineers.