The world’s population and economy are growing rapidly, resulting in an increasing demand for natural resources and increasing risk of environmental damage. Excessive use of natural resources such as water, land and forests affects the livelihoods of many people and national economies. Similarly, environmental damage can affect current and future economic and social development. In other words, the economy, society and the environment are interlinked issues. So, if you want to solve one of these problems you need to consider all three together, because addressing only one aspect either will not solve the problem in the long term, or it will create another problem. This is the concept of sustainability, which you are going to look at in this study session. We will also discuss different interpretations of development including economic, human and sustainable development and discuss the sustainability of WASH services.