This book is a comprehensive guide to water desalination, addressing the global freshwater crisis exacerbated by population growth and climate change. It focuses on reverse osmosis methods, outlining technical, economic, and environmental challenges, and proposes performance evaluation methodologies like ROPI and ROEPI. The text emphasizes water quality, system efficiency, and the integration of AI and simulation technologies to enhance operational efficiency. It also discusses the economic implications and environmental impacts of desalination. Ultimately, it advocates for sustainable practices and partnerships to ensure effective freshwater management.