Hydraulic weighing lysimeters can be a reliable and relatively inexpensive source of actual crop evapotranspiration (ET) data for field water use studies and crop coefficient development. However, the reliability, quality and accuracy of the data obtained with these systems will depend on the care taken in construction and installation as well as field operation and maintenance thereafter. Hydraulic weighing lysimeters have been described by Hanks and Shawcroft (1965), Tanner (1967), Dylla and Cox (1973) and McFarland et al. (1983). Several different designs and improvements have been made on these systems over the years. The data and observations in this manuscript will refer to a paired lysimeter system designed at USDA-ARS and described by Kincaid et al. (1979). The objectives of this paper are: (1) to describe field experience with hydraulic weighing lysimeters installed in the Grand Valley and San Luis Valley of Colorado; (2) discuss problems and outline proper operation and maintenance required for quality data collection.