To account for the weight of the ponded water, while having zero pore pressure in the slope, set the Water Surface to None in the Define Materials Properties dialog.
Define Material Properties dialog
If the water table is above the ground surface, ponded water is automatically created and the weight of the water is added to each slice, regardless of whether it creates pore pressure in a material. To see this, simply look at the slice weights by turning on the slices.
If you want a different pore pressure distribution in the foundation material then what would be given by the water table, you need to use piezometric lines. You define a piezometric polyline in a similar way as the water table but at a different location. You can then apply that piezometric line to any material. To add a piezometric line, go to the boundaries menu in the Slide modeler.