While water consumption and water conservation have been issues in the discussion of sustainable tourism for many years, the residual part of the water cycle, the management of wastewater, lacks attention in tourism and planning research. This study addresses the wastewater challenges in Danish second home tourism. More than 200,000 second homes represent an important touristic resource both for owners and for short-term renters, and increasingly, the accommodation capacity is used over the whole year. Data from the building and housing register (BBR) show that only 54% of second homes are connected to public sewage and purification utilities. The remaining second homes rely on individual solutions such as septic tanks. A substantial regional variance can be partly explained by differences in the spatial layout and location of second homes, but mainly the dissimilar priorities in the responsible municipalities are the result of systemic factors following semi-privatized governance structures. The intensified use of second homes, rising ground water levels, more frequent climate incidences and EU and national quality obligations for the environmental standards of waterways and seas are and will in the future be challenges for the municipal wastewater management. A mobilization of second home owners and users to support updated wastewater infrastructures is hampered by the principles laid down in the governance structures.