In older versions of SLOPE/W, soil layers were developed using soil lines that corresponded directly to the order in which the soil layers were initially defined. As a result, adding water as an after-thought to an existing analysis was a little complicated. The pressure boundary approach made it relatively easy to add a water layer after a profile had already been developed. In GeoStudio 2004, the constraints of how and when soil layers can be added to an analysis no longer exist, so a water layer can be easily added at any point in an analysis.
In GeoStudio 2004 (V6.21 or greater), a water layer should be modeled as a no-strength soil with the unit weight of water, not as a pressure boundary. Modeling water as a pressure boundary will only work when side slopes are non-vertical. If a pressure boundary is used to represent water against a vertical wall, the pressure boundary will not exert a horizontal hydrostatic force against the wall. Only modeling water as a soil layer that has been assigned a no-strength soil model (with the unit weight of water) will properly represent the horizontal force that water will apply on a vertical face. Both a pressure boundary and water modeled as a no-strength material can be used on non-vertical slopes, but since the pressure boundary option is not appropriate for all situations, it is good modeling practice to always model water using a no-strength material.
In addition to the creation of a water layer, a piezometric line will need to be drawn across the surface of the water and through the profile. The water layer models the weight of the ponded water and the piezometric line is used to compute the pore-water pressures that exist at the base of each slice.