This book aims at presenting a unified framework for the description of working principles, recent advances and applications of cutting-edge measurement technologies for the water sector. Instrumentation and measurement technologies are currently playing a key role in the monitoring, assessment and protection of environmental resources. Measurement techniques and sensing methods for the observation of water systems are rapidly evolving and are requiring an increased multi-disciplinary participation. The whole water sector is characterised by multiple technological contexts concerning the monitoring of the resource, given the broad coverage that includes water from its natural domains to the men-made infrastructures. In particular, instrumentation and measurement technologies have a pervasive presence in all the necessary aspects for the assessment, monitoring and control of the water resource and of its relationship with the various environmental stressors, including the anthropic pressures. Therefore, the book aims at presenting how the diagnostics/monitoring methodologies and the related technologies can give an answer to the issues raised by the complex scenario characterising the water cycle management (WCM). The book is structured in five topical sections, grouped by similarity of their technological and/or applicative contexts.