Abstract. The aim of the study was to evaluate catchment area impact on small water reservoirs condition in Podlasie. The researches were conducted in two different catchment areas. Topiło reservoir, located in Podlasie area in the south-east of Białowieża Forest, has typical sylvan catchment. Second reservoir, Dojlidy, is located also in Podlasie, in the south-east of Białystok as a part of Dojlidy Ponds. In contrast to Topiło, Dojlidy has agricultural catchment. Water samples collected from five sites along each reservoir were analysed for the presence of total nitrogen and phosphorus, chlorophyll "a", reaction, turbidity and conductivity. Researches took place in spring, summer and autumn 2013 (Topiło Lake) and 2014/2015 (Dojlidy). The lowest trophic state was observed in autumn and the highest in summer. Because of the high loads of phosphorus received by the reservoirs, this element did not limit primary production. Calculated TSI values based on total phosphorus were always markedly higher than calculated on chlorophyll-a and total nitrogen. Both reservoirs demonstrated TSI indexes specific to hypertrophic lakes due to large amount of total phosphorus.

The costs for piping comparisons should include both the costs of the materials as well as construction. The construction costs depend on the trench depth, type of the soil, presence of rock, type of bedding material or location (urban and rural areas). The average costs of pipes were analysed in the article depending on material type, diameter and trench depth. The data relating to the pipe prices were collected on the basis of BISTYP cost base. Moreover, a preliminary analysis of sewage and water supply system cost was made on the basis of technical documentations published in Public Information Bulletins of communes. Recently, there has been a significant increase of interest in plastic pipes. Due to the low price and availability, these materials are most common used during piping both rural and urban areas.

Rural areas, similar with the amount of produced sewage to urban areas, are rarely parts of agglomerations. Because of dispersed buildings and often poor infrastructure, sewage management regulation in rural areas can be difficult. Caring for the environment include aquatic environment protection. Sewage economy regulations, especially in rural areas, is a key issue in water contaminations counteracting. Often inappropriate sewage disposal and treatment methods choice could cause ecological imbalance and water pollution as the result. The aim of this paper was to evaluate water and sewage economy development in Sokólski District in Poland. In the study were used Central Statistical Office of Poland data from 2008–2016. There was considered cesspit and household sewage treatment plants amount and water and wastewater systems length. Also, sewage systems built in recent years and planned in the analysed area were considered. In recent years reducing trend in a number of cesspits was observed. In 2008–2016 there was an increase in a number of household sewage treatment plants by 919 and about 50 kilometres of the sewage system, while there were 400 cesspits less.

The aim of this article was to evaluate the water and sewage economy development in Podlaskie Voivodeship in comparison to the rest of the country. Moreover, the best developing districts in analysed area have been marked out. The data from Central Statistical Office of Poland from 2008-2015 pertaining to a range of waterworks, sewerage and sewage plants was used in the study. In recent years we have observed a decreasing tendency in the number of cesspits in favour of sewage systems and household sewage treatment plants. In 2008-2015 water and sewage economy in Poland was expanded in 150 840 Household Sewage Treatment Plants and 54 876.4 km of sewage systems. Podlaskie Voivodeship assumed 12 th place in the country in respect to newly built waterworks (advancement by one position) and the last place in respect to sewerage length.

The main aim of the research was to analyze expenditures for sewage management and water protection and to identify Polish commune types that are characterized by the highest expenses. The analyses were made using classification trees in Statistica software (Dell Statistica (data analysis software system), version 13, Dell Inc., Round Rock, TX, USA). For this purpose, a database consisting of seven independent variables was prepared.