The purpose of this paper is to analyze the implementation of investments in the water and sewage sector in Poland and other European countries using the Public-Private Partnership (PPP) formula. The paper identifies the strengths and weaknesses, opportunities and threats arising from the use of this formula for local government public tasks for the delivery and treatment of domestic wastewater, in the context of EU legislation. It also examines the validity of the use of PPP in the context of the implementation of the principle of sustainable development in water management. PPPs are commonly used to deliver strategic public services under financial limitations. Countries such as the United Kingdom and Ireland, based on years of experience and good practices, are effectively implementing PPP projects, including those in the water and sewerage sector. The provision of treated drinking water and the treatment of municipal wastewater is a fundamental task ensuring an adequate quality of life for people by maintaining public health at an appropriate level. The fact that water and sanitation infrastructure and service provision in this sector is expensive, both at the construction and operational stages, has led countries at different levels of development to turn to public-private partnerships. Properly managed PPP projects secure the interests of both the private and public partner and the end user of the services. The analysis of data and examples of European PPPs in the water and wastewater sector shows that PPPs have been successful for most public entities that have chosen them. Good practices from Scotland, Ireland and Poland, as well as projects that have experienced difficulties, show that stable and friendly legislation, thorough pre-feasibility studies and an appropriate allocation of risk make PPPs successful. In the context of the conducted analysis, PPP is a tool enabling the realization of tasks in the water and sewage sector, where the public party’s budget possibilities are limited. Moreover, PPP is a component of the realization of the sustainable development principle. The idea that the use of natural resources, including water, which is fundamental to the biological and cultural needs of humankind, should be met in such a way as to save them for future generations, is realized in PPP projects. This paper demonstrates that the use of financial assembly opportunities in PPPs makes it possible to significantly intensify the construction of new and upgrading of existing water and wastewater infrastructure. It contributes to the protection of aquatic ecosystems and securing public health associated with living in direct proximity to surface water and discharging wastewater without affecting the natural environment and human habitats.