Summary:

The problem of hydraulic underloading of sewage treatment plants in ru-ral areas concerns currently many objects. It results from several basic facts, i.e. lack of collective systems of sewage removal or assuming too large volume of in-flowing sewage assumed in a treatment plant construction project. It seems that extension of sewer systems in rural areas seems a matter of time, which will allow to supply much bigger volume of sewage to the treatment plants. On the other hand proper reception of the amount of inflowing sewage is the most complex problem. Currently the most frequently quoted value per capita is 150 dm³∙M^-1 of consumed water (discharged sewage) daily. In fact these amounts are often over-estimated whereas real amount of water used is much lower. The paper attempts at comparing the volume of outflowing sewage in com-parison with values planned in the project. The research comprised four house-hold sewage treatment plants situated in rural districts in the malopolskie province. In the Turbojet EP-2 treatment plant sewage inflow during the research period was 0.82 m³∙d^-1 and lower than assumed (1.5 m³∙d^-1) by 46%. In the Tur-bojet EP-4 the real sewage inflow was on average 0.81 m³∙d^-1, which constituted only 19% of the inflow planned in the project. In the Biocompact BCT S^-1 sewage treatment plant amount of inflowing sewage was on average 0.5 m³∙d^-1 and lower than assumed (0.6 m³∙d^-1) by 17%. In the last analyzed object Biocompact BCT S-12 assumed sewage inflow was on the level of 12 m³∙d^-1, whereas the real inflow amounted to 5.0 m³∙d^-1 and was lower than the projected inflow by 47%. During the research period all analyzed objects were hydraulically under-loaded. The difference between the actual and projected inflow ranged between 17% and 47%.