Water treatment operator study guides are hard to come by, at least ones that adequately prepare you to take the certification exam. Here's a list of some of the best online resources I've compiled over the last several months as I've been studying for the operator's exam.
If you have any you would like to add please leave a comment below.
The Training Station - Published by the Tennessee Association of Utility Districts, the Certification Study Guide for Water Treatment was designed to help water treatment operators prepare for certification exams. This 157 page pdf file is packed with information on ground water, sterilization, fluoridation, chemical feeders, pumps and motors, algae, coagulation & flocculation, filtration and more.