While most other network industries, such as the telecommunications sector or the aviation sector, were opened for competition years ago, the water sector remains the last bastion of vertically integrated monopolies. This book analyzes the potentials and limitations of different options for competition in the water sector, consistently applying the disaggregated approach of network economics. A special feature of the sector is the crucial importance of ensuring a non-hazardous quality for drinking water. Therefore a precise definition of the term 'good water quality' is developed. On this basis the impacts on water quality due to the introduction of competition are reviewed. The analysis is illustrated by several international case studies.