The prosperity of Egyptian civilization has depended on the efficient use of water deriving from the Nile throughout its recorded history. Despite the importance of water and irrigation in ancient Egypt, very little is known of its water regulations. The only known legal source related directly to the maintenance of canals that has been preserved is a section of the Dikaiomata – the Alexandrian city law dealing with the construction and improvement of irrigation channels in the surrounding countryside. However, being Greek in origin, it does not seem to correspond to the legal practice that has been in use in Egypt since the earliest times. How water regulations looked like in practice can therefore only be observed by means of practice documents, i.e. papyri from Ptolemaic period. Such papyri recorded the law in action, both in relation to individuals as well as the whole society in the context of water management. These documents and their similarities and differences to the rules contained in Dikaiomata are the subject of the paper.