The recent history of water supply and sanitation projects in developing countries offers many varied examples of approaches assumptions, beliefs and patterns - otherwise called paradigms - regarding initiation, decision-making, design criteria, financing , and the management of operation and maintenance. These paradigms are like the roots of ta tree in that they form the foundation and determine the nature and sustainability of a project. The tasks of making wholesome drinking water and satisfactory sanitation available to everyone remain huge and challenging, and it is important that efforts in this connection are based on the best possible foundations. This booklet has been derived from presentations and discussions at an Aguasan workshop. It includes an explanation of the importance of paradigms, suggestions for investigating and modifying paradigms, and examples of processes of reviewing and modifying paradigms, based on case studies from Africa and Asia. The examples show how new paradigms can lead to radically new - and potentially better - solutions.