Biomethane is an easily storable, renewable energy source that is applicable to the sectors electricity, heat, and transport. It is mostly obtained from biogas by different upgrading technologies. At present, the most common technology is water scrubbing because of its reliability and simplicity. A methodology for designing as well as for evaluating and optimizing water scrubbing plants including biomethane compression is introduced. To demonstrate possible applications of this methodology, a zero-emission water scrubbing process characterized by under-pressure regeneration of washing water is modeled and investigated by a sensitivity analysis.