Water is one of the most precious and basic needs of life for all living beings, and a precious national asset. Without it, the existence of life cannot be imagined. Availability of pure water is decreasing day by day, and water scarcity has become a major problem that is faced by our society for the past few years. Hence, it is essential to find and disseminate the key solutions for water quality and scarcity issues. The inaccessibility and poor water quality continue to pose a major threat to human health worldwide. Around billions of people lacking to access drinkable water. The water contains the pathogenic impurities; which are responsible for water-borne diseases. The concept of water quality mainly depends on the chemical, physical, biological, and radiological measurement standards to evaluate the water quality and determine the concentration of all components, then compare the results of this concentration with the purpose for which this water is used. Therefore, awareness and a firm grounding in water science are the primary needs of readers, professionals, and researchers working in this research area. This book explores the basic concepts and applications of water science. It provides an in-depth look at water pollutants' classification, water recycling, qualitative and quantitative analysis, and efficient wastewater treatment methodologies. It also provides occurrence, human health risk assessment, strategies for removal of radionuclides and pharmaceuticals in aquatic systems. The book chapters are written by leading researchers throughout the world. This book is an invaluable guide to students, professors, scientists and R&D industrial specialists working in the field of environmental science, geoscience, water science, physics and chemistry.