In many sparsely populated areas, such as the Finnish countryside, most houses are not connected to
centralized sewers due to excessive distances. On-site wastewater treatment plants are therefore
necessary to reduce local emissions to meet the legislatory limits. Dozens of on-site wastewater treatment
applications are marketed to households, with varying operating costs and pollution reduction
potentials. The installation and use of these systems will cause environmental impacts outside the site,
through their supply chains. The aim of this study is to analyze the potential tradeoff between the
reduction of local emissions and the increase in life cycle impacts. Six alternatives were chosen for
comparison, including the energy-demanding small sewage treatment plants and the various types of
soil systems (including source separation systems). The results show that the dry toilet in combination
with gray-water treatment had the least impact and the package plants the greatest. However, which is
the optimal on-site system solution for a certain property is strongly dependent on the local conditions
and, therefore, appropriate guidance is definitely needed.