Wastewater Treatment Operator Certification (US, Class I to IV)

Each certifying authority chooses which exams it gives, and each certification program decides the content of its own exams. Some programs use the standardized Wastewater Treatment Operator exams of Water Professionals International (WPI), delivered by its testing service, ABC Testing, in four classes, I to IV. WPI's 2025 Need-to-Know Criteria for the Class I to IV exams group the content into four areas: Equipment Evaluation, Maintenance, and/or Operation; Treatment Process Evaluation and Adjustment; Laboratory Analysis; and Security, Safety, and Administrative Procedures. Each exam has 100 scored questions and may include up to 10 unscored pre-test questions. The exams are multiple choice, include calculation questions shown in US standard and metric units, and are administered with a Formula/Conversion Table.