Water and sewage management in Poland has systematically been transformed in terms of quality and quantity since the 1990s. Currently, the most important problem in this matter is posed by areas where buildings are spread out across rural areas. The present work aims to analyse the process of changes and the current state of water and sewage management in rural areas of Poland. The author intended to present the issues in their broader context, paying attention to local specificity as well as natural and economic conditions. The analysis led to the conclusion that there have been significant positive changes in water and sewage infrastructure in rural Poland. A several-fold increase in the length of sewage and water supply networks and number of sewage treatment plants was identified. There has been an increase in the use of water and treated sewage, while raw sewage has been minimised. Tap-water quality and wastewater treatment standards have improved. At the same time, areas requiring further improvement—primarily wastewater management—were indicated. It was identified that having only 42% of the rural population connected to a collective sewerage system is unsatisfactory. All the more so, in light of the fact that more than twice as many consumers are connected to the water supply network (85%). The major ecological threat that closed-system septic sewage tanks pose is highlighted. It is pointed out that they are mainly being replaced by household wastewater treatment systems with ineffective filtering drainage. Furthermore, recommendations were also made for the future development of selected aspects of water and sewage management, including the legal and the political.

Lake waters are a significant source of drinking water and contribute to the local economy (e.g. enabling irrigation, offering opportunities for tourism, waterways for transport, and meeting utility water demands); therefore, the ability to accurately forecast lake water levels is important. However, given the significant lack of research with respect to forecasting water levels in small lakes (i.e. 0.05 km² < area < 10 km²), the present study sought to address this knowledge gap by testing a pair of hypotheses: (1) it is possible to forecast water levels in small surface lakes using artificial neural networks (ANN), and (2) better water-level forecasts will be obtained when the wavelet transform (WT) is used as an input data pre-processing tool. Based on an analysis of a case study in Lake Biskupinskie (1.16 km²) in Poland and based on a range of model performance statistics (e.g. mean absolute error, root mean square error, mean squared error, coefficient of determination, mean absolute percentage error), both hypotheses were confirmed for monthly forecasting of lake water levels. ANNs provided good forecasting results, and WT pre-processing of input data led to even better forecasts. Additionally, it was found that meteorological variables did not have a significant impact in forecasting water-level fluctuations. In light of the results and the limited scope of the present study, proposed future research directions and problems to be resolved are discussed.

The aim of this study is to assess the possibility of forecasting water level fluctuations in a relatively small (<100 km2), post-glacial lake located in a temperate climate zone by means of artificial neural networks and multiple linear regression. The area of study was Lake Serwy, located in northeastern Poland. Two artificial neural network (ANN) multilayer perceptron (MLP) and multiple linear regression (MLR) models were built. The following explanatory variables were considered: maximal and minimal temperature (Tmax, Tmin) wind speed (WS), vertical circulation (VC) and water level from previous periods (WL). Additionally, a binary variable describing the period of the year (winter, summer) has been considered in one of the two MLP and MLR models. The forecasting models have been assessed based on selected criteria: mean absolute percentage error (MAPE), root mean squared error (RMSE), coefficient of determination (R2) and mean biased error. Considering their values and absolute deviations from observed values it was concluded that the ANN model using an additional binary variable (MLP_B+) has the best forecasting performance. Absolute deviations from observed values were the determining factor which made this model the most efficient. In the case of the MLP_B+ model, those values were about 10% lower than in other models. The conducted analyses indicated good performance of ANN networks as a forecasting tool for relatively small lakes located in temperate climate zones. It is acknowledged that they enable water level forecasting with greater precision and lower absolute deviations than the use of multiple linear regression models.

Energy system research requires input data with high temporal and spatial resolution. However, the measurements performed in meteorological stations are only available for selected locations. Currently a growing number of research papers on small and large-scale power systems utilizes data coming from satellite measurements and various reanalyses. Although many authors aimed at comparing various data sources on irradiation and wind speed there is a lack of such studies, which compare both resources simultaneously at the same location. In consequence, many studies which are entirely based on satellite/reanalysis data may not be representative. In this paper 15 locations in Poland have been selected where the National Institute of Meteorology and Water Management performs continuous measurements of wind speed, temperature and global irradiation on a horizontal surface. Hourly time series were obtained for the year 2012 and 2013. The renewable resources were converted into electrical energy, considering the performance of typical PV panels and wind turbines. The findings of this study are as follows: solar radiation (CAMS and ERA5) shows a good agreement with ground measurements, for hourly values the coefficient of correlations is greater than 0.9; for individual locations the energy yield from PV system can differ by up to 9% but on average (all locations) the simulated energy yield based on satellite data is higher by less than 0.5%; simulations for wind energy showed a large variability in results with differences in capacity factors reaching 15 percentage points.

This paper presents changes in water and sewage management in the cross-border Oder River basin in the period since the post-communist political and economic system transformation, including the period after Poland’s accession to the European Union. The Oder River basin, with an area of 124,000 km², is the second largest basin in the Baltic Sea Basin, and therefore requires particular protection. It was emphasised that in the years 1989–2017, water withdrawal for production purposes considerably decreased (by 42%), as well as water withdrawal for exploitation of the water supply system (by 33%). The amount of sewage discharged to rivers was also reduced (by approximately 50%), and treatment technologies considerably improved. Changes in water and sewage management were presented in spatial form, i.e. by hydrographic regions of the Oder River basin. Particular attention was paid to changes in sewage management in cities. They involved among others the liquidation of mechanical treatment plants and a considerable increase in the number of cities with treatment plants with increased nutrient removal. The analysis of the effect of the changes in water and sewage management on the quality of the Oder River and Baltic Sea was also performed, and the rate of decrease in loads of contaminants most harmful to water ecosystems was determined. The role of European Union funds and national funds in the implementation of investments in the scope of water management was emphasised. Finally, attention was drawn to the need to intensify works for protecting waters in agricultural areas, which currently constitute the primary threat to their quality. Several top-priority tasks were also specified that should be implemented in the near future for the purpose of obtaining a good ecological state of waters in the Oder River basin pursuant to the Water Framework Directive.