Water is essential for life. An adequate, safe and accessible water supply must be available to all people, and improving access to safe drinking water can result in tangible benefits to health. Water is one of the factors which contribute to the transmission of many diseases. In this study session, you will learn and understand about the public health importance of water, the water (hydrological) cycle, the basic requirements for a safe, adequate and accessible drinking water supply, and the obstacles to safe water provision. You will also learn about different indicators for safe, adequate and accessible water supply. This study session will help you to recognise the basic requirements for safe water supply and to understand the transmission of waterborne diseases.