The aim of the article was to determine the feasibility and advisability of the use of secondary filters applied before discharge of wastewater into the ground in the context of the fulfillment of the conditions of the current Regulation of the Minister of Environment of 18 November 2014 on the conditions to be met during the discharge of wastewater into the water or the ground and on substances particularly harmful to the aquatic environment. Due to expected in practice, an application and popularity, as compared variants, reactors having a very simple construction were used. The average values of removal of BOD₅, COD and total suspended solids for three secondary filters technologies: biological trickling filter with natural ventilation, sand filter and nonwoven filter were compared. Additionally, as a fourth option a simple mathematical model has been presented. This model allows to estimate of BOD₅ at the outflow from biological trickling filter and to verify the empirical data. Despite a large usefulness, it is rarely used in our country. It has been found the possibility of reduction of the infiltration area (surface area after reduction is 38–63% of the initial value) due to the application of secondary filters. In the case of a high initial demand of the terrain area for drainage localization the benefit in costs resulting from the reduction (several thousand of PLN) or may even significantly exceed the cost of buying and installing a cheap secondary filter. In addition, reduction the occupied area of the lot (in extreme cases up to 100 m²) by using the secondary filter allows to use the unoccupied space for other purposes, and thus gives additional economic advantage.