Environmental sustainability demands the advancement in water treatment and the use of lighting natural resources. Brazil has one of the most stable and intense solar irradiation in the world. It has to be used not only for energy generation purposes but also and mostly for water treatment, water quality polishment, and furthermore water disinfection. The chapter performs a comparison of different green technologies for water treatment as natural solar irradiation, simulated solar photolysis, solar photo-Fenton with and without hydrogen peroxide addition (solar/ Fe), solar photo-Fenton with and without peroxide (solar/Fe/H2O2), titanium oxide-mediated photocatalysis (UV/TiO2), photolysis under UV irradiation, and UV treatment with hydrogen peroxide (UV/H2O2). The chapter describes the solar photodecomposition calculations for pharmaceuticals and the emerging pollutants mostly found in polluted waters, including the decomposition route, kinetics, and process parameters. Many published works to point out the important properties to evaluate catalyzer and semiconductor materials after their use in photodecomposition processes. The essay includes the solar photodecomposition of dyes, carbamazepine, hormones, acetaminophen, antipyrine, bisphenol A, antibiotics, and the photodecomposition by-products. Finally, the chapter presents the synergistic effect between them with the probable mechanism and mineralization degree.