Decentralized water systems are perceived as solutions that not only save water, but also as a way to partially or completely become independent from centralized suppliers. Taking this into account, an analysis of the effectiveness of rainwater harvesting systems (RWHS) for toilet flushing in existing academic facilities located in Poland and in Slovakia was carried out. The tests took into account the different volumes of storage tanks collecting rainwater. On the basis of two financial ratios, namely Net Present Value and Discounted Payback Period, the profitability of these systems was also assessed. The research was extended by the sensitivity analysis, which allowed determination of the impact of changes in individual cost components on the financial effectiveness of the investments considered. The results obtained clearly showed that the implementation of RWHS in the dormitory in Rzeszów was unprofitable for all tank capacities tested, and the payback period significantly exceeded the period of 30 years accepted for the analysis. Completely different results were obtained for RWHS in a dormitory located in the city of Košice, for which the financial ratios NPV (Net Present Value) and DPP (Discounted Payback Period) were very favorable. It was also confirmed by the results of the sensitivity analysis. The use of rainwater for toilet flushing caused that it was possible to achieve water savings of an average of 29% and 18%, respectively, for facilities located in Slovakia and Poland. The results of the research have a practical aspect and can provide an indication for potential investors and managers of academic facilities, similar to those analyzed in the article. Taking into account that in many countries water and sewage rates are significantly higher than in Poland and Slovakia, the cost-effectiveness of using the analyzed installation options in these countries could be even higher.

World population growth, climate changes, urbanization, and industrialization have all had a negative impact on natural resources, including water resources. Excessive exploitation and pollution have caused more and more regions to have problems with access to fresh water. Rainwater is perceived as a valuable alternative source of water that is most often used in a hybrid system supplementing tap water. Considering the possibilities of designing a rainwater harvesting system as a decentralized or central system, this research was undertaken to determine the hydraulic and financial efficiency of these two systems. The research was carried out for a single-family housing estate located in Poland. For this research, a simulation model was applied to determine the efficiency of water saving and the life cycle cost indicator. In variants where rainwater was only used to flush toilets, the water saving efficiency was 80% and 79% for the decentralized and centralized rainwater harvesting system (RWHS), respectively. The use of rainwater for toilet flushing and watering the garden resulted in a significant reduction in efficiency to 57% (the decentralized system) and 54% (the centralized system). On the other hand, the results of the life cycle cost (LCC) analysis showed that in spite of reducing tap water consumption, both the centralized and the decentralized rainwater harvesting system were not financially viable solutions for the housing estate, and only cofinancing investments at the level of 25% to 50% resulted in a significant improvement in financial efficiency.

The aim of the paper was to identify factors that influence the public perception of the possibility of replacing tap water with rainwater or greywater. In order to check whether a geographical location and water resources of a region affect the public's attitude toward alternative water systems, the surveys were carried out among respondents from twelve countries. The surveys identified the level of awareness among respondents about their country's water resources, ways to save water at home, and their attitudes to rainwater and greywater as additional sources of water in a building. The results showed that only 39% of respondents would not be afraid to use treated greywater in their household. The situation was better in case of replacement of tap water with rainwater, where more than 54% of the respondents were not concerned. The use of alternative sources of water for body washing and cleaning works was the biggest concern among the respondents. In case of greywater recycling, this was indicated by 56% (personal hygiene) and 34% (cleaning works) of respondents. People in the countries with low water resources view alternative water sources more favourably. They are also more aware of, and more likely to accept the use of rainwater or greywater even in uses where they will come into contact with the human body. The research also showed that for more than 3/4 of respondents, funding to install these systems would encourage their use in their household.

The article contains the outcomes of the Life Cycle Cost analysis for alternative energy and water sources utilized in passive buildings. The solutions taken into account included: heat pumps, solar collectors, photovoltaic panels, Drain Water Heat Recovery units, Rain Water Harvesting Systems and Greywater Recycling Systems. In addition, air pollution emission reduction was also calculated for all the installation variants analyzed. The analysis have shown that the systems under consideration could serve as alternatives for traditional installations. Their use has resulted in reductions in the consumption of fossil fuels and natural water resources, thus contributing to environmental improvements.