Using a new test setup, the results for the mechanical impact force and pressure of water jets of a nozzle in tubular form with different nozzle diameters (3, 4 mm), gauge pressures (1 - 6 bar) and stand-off distances (0.5 - 5 m) are presented. It is shown that the stand-off distance and, thus, the jet break-up has a significant influence on the mechanical forces of water jets. An optimum stand-off distance with regard to the maximum impact force and pressure was determined in the range of 2 - 2.5 m. As a result, a semi-empirical equation for the description of the mean impact force was derived.