WPI standardized operator exams

Water Professionals International (WPI), formerly the Association of Boards of Certification (ABC), publishes standardized water and wastewater operator exams. Many states use them, but each state chooses its own exams, class names, time limits, and passing scores.

A WPI-format exam has 100 scored multiple-choice questions plus up to 10 unscored pretest questions. Content areas and weights below come from WPI’s published Need-to-Know Criteria (2025) where we have read the document, and are listed without percentages where we have not. Last checked October 10, 2026.

This site is independent and is not affiliated with WPI or ABC. Confirm which exam your state uses with your certifying agency.

Water Treatment Operator

Class I
Content areas with weights
Class II
Content areas with weights
Class III
Content areas
Class IV
Content areas with weights

Water Distribution Operator

Class I
Content areas with weights
Class II
Content areas
Class III
Content areas
Class IV
Content areas

Wastewater Treatment Operator

Class I
Content areas with weights
Class II
Content areas with weights
Class III
Content areas with weights
Class IV
Content areas with weights

Wastewater Collection Operator

Class I
Content areas with weights
Class II
Content areas
Class III
Content areas
Class IV
Content areas