Structure-borne sound generated by wastewater pipe systems often dominates noise emissions from sanitary installations in buildings. This paper presents a preparatory investigation aimed at estimation of the water excitation terms by the inverse method. The experimental setup followed EN 14366-1:2023 and the vibration response of the pipe was quantified in terms of the blocked force at the wall fixing points. Noise from wastewater systems is generated by turbulent annular flow and the impact of water at the inlets, tees, and bends. These excitation terms were estimated through a methodical, stepwise approach. First, a customized impact-free inlet was installed to the pipe to eliminate water inlet effects, and thus the annular flow served as the primary excitation source in a straight pipe configuration. Subsequently, the impact of the flow turning elements was evaluated. The numerical model of the drainpipe was then introduced and experimentally verified. Using this model, the inverse method was tested to indirectly identify the applied force acting on the pipe. These presented results serve as the essential basis toward the development of a mathematical model of the stochastic water loads applied to the pipes.