Ensuring sustainable consumption of water, which is essential for human development, is not sufficient, therefore, there is an urgent need to improve reuse of treated wastewater. This paper reviews the newest EU legislation related to reclaimed water reuse, which is the main driver for change. While there are some positive developments in the EU, the paper argues that the current EU legislation does not sufficiently encourage circular solutions, especially on how to deal with any bottleneck effects, which prevent to fully utilise wastewater. This reflection is noted based on the national and regional developments in Italy with some comparison with other Southern countries, such as Greece and Spain in attempt to identify good practices as well as any barriers for the reclaimed water to be reused.

Solar thermal energy represents a mature and versatile pathway for harvesting solar radiation in the form of useful heat across a wide range of temperature levels. Unlike photovoltaic-based technologies, solar thermal systems directly address thermal energy demands in residential, industrial, and power-generation sectors, which constitute a substantial share of global energy consumption. This review presents a structured overview of solar thermal technologies and their practical applications using a temperature-oriented perspective rather than a conventional collector-based classification. Solar thermal systems are categorized according to their delivered heat quality, spanning low-, medium-, and high-temperature regimes, and the functional role of different collector concepts within each regime is discussed. The review further maps these temperature ranges to key application domains, including domestic heat supply, industrial process heat, solar-driven desalination, cooling technologies, and concentrated solar power systems. In addition, critical design and integration aspects such as thermal losses, heat transfer fluids, storage compatibility, and system-level challenges are examined. By reorganizing existing knowledge around heat demand and operating temperature, this review aims to provide clear guidance for researchers, engineers, and practitioners seeking to select and integrate appropriate solar thermal solutions for specific applications.