Water is central to human existence and promotion of healthy living, hence the saying that "water is life". Use of water by man, plants and animals is universal. Human community uses water for various purposes and in the end produces both liquid and solid wastes as well as air emission. The liquid waste normally referred to as wastewater has its major parts coming from the water, people have consumed. Those wastes are to be disposed off at suitable places so as to ensure proper sanitation. The book discusses the concepts involved in the process of water supply, wastewater treatment as well as the principles of sanitation. The book is divided into two parts with each part consisting of seven chapters. Each chapter is also divided into sections and sub-sections. Part I of the book deals with water supply while Part II is devoted to wastewater treatment and sanitation. Worked examples are given where applicable and at the end of each chapter, practice questions are given. The book is written for practitioners in the fields of civil engineering, environmental engineering, public health and water resources. It will be particularly useful for students in those fields of study.