The first part of this series focused on the work of Jacob Leupold, the second part on the work of Leonhard Thurneysser and Torbern Berman, and the third part on the work of Pierre-Joseph Macquer and William Thomas Brande. This fourth and last part completes the picture of premodern water ‘know-how’. A German, a French and three English encyclopedias from the 18th century are presented and their value as sources is examined. Of particular interest is the question of the form in which chemical knowledge was incorporated into the lexicon articles. It is a matter of speculation whether the encyclopedias contributed to popularizing knowledge about water.