The masterful study of the institution of waqf in Zaydi Yemen by Eirik Hovden is available to download in open access from Brill. Based on both ethnographic fieldwork in Yemen and analysis of relevant Islamic texts, this is an important resource for anyone interested in the history of the Zaydis in Yemen. An Arabic translation is in progress.
Here is a brief note by the author on the purpose of his book:
"As a thematic focus, this book concentrates on 'non-mosque' public foundations in Yemen and most of the examples are related to the public water supply. Water supply serves as a typical example of the non-mosque related services that the institution of waqf was a vehicle for. Water supply is also a type of service, or public infrastructure central to both Yemeni and western development discourses and thus it is a shared, common focus that transcends the secular/religious divide or the divide between Islamic studies, history, and development studies. This book provides a legally oriented ethnographic description of a truly local mode of management of public resources—a local mode that should not be overlooked in the ongoing quest to find locally accepted legal and political vehicles for managing public, common good."