Wastewater Treatment Operator Class I Exam Pass Rate, Format & Study Guide

The Wastewater Treatment Operator Class I exam is a standardized certification exam used by many state wastewater operator certification programs. It is developed and scored by Water Professionals International (WPI) through ABC Testing, and your state certification program decides whether you qualify. The exam is a standardized multiple-choice exam whose competencies are listed in the WPI Need-to-Know Criteria; the number of questions and time allowed are set by your state program. This portal's practice mock has 100 questions.

State programs certify wastewater treatment plant operators, and many use the WPI/ABC standardized exams. Passing the exam is a required step toward the operator certificate.

Entry-level wastewater operators and trainees preparing for a Class I certification exam and candidates retaking it. State requirements vary; check your state program.

The certifying body does not publicly publish an official pass rate for this exam. Be wary of third-party sites citing a specific number here — treat any pass-rate claim you see elsewhere for this exam as unverified.

Your state certification program sets the retake rules, fees and waiting periods.

Passing standard: ABC/WPI states that a passing score of 70 percent or above is required on certification exams (WPI, search extract). The exam is a standardized multiple-choice exam whose competencies are listed in the WPI Need-to-Know Criteria; the number of questions and time allowed are set by your state program. This portal's practice mock has 100 questions. No official pass rate for this exam was available in the sources we reviewed, so none is quoted here.

The exam is a standardized multiple-choice exam whose competencies are listed in the WPI Need-to-Know Criteria; the number of questions and time allowed are set by your state program. This portal's practice mock has 100 questions. Format: Standardized multiple-choice exam (ABC Testing / WPI) · Class I is the entry level of four classes (I-IV) · this portal's practice mock: 100 questions. Passing standard: ABC/WPI states that a passing score of 70 percent or above is required on certification exams (WPI, search extract).

• Equipment Evaluation, Maintenance, and/or Operation39%
• Treatment Process Evaluation and Adjustment38%
• Laboratory Analysis10%
• Security, Safety, and Administrative Procedures13%

The content outline spreads questions across 4 areas: Equipment Evaluation, Maintenance, and/or Operation (39.0%); Treatment Process Evaluation and Adjustment (38.0%); Laboratory Analysis (10.0%); Security, Safety, and Administrative Procedures (13.0%).

Your state certification program sets the education and experience requirements for each class and approves you to sit the exam; confirm them with your state program before you apply.

Exam and application fees are set by your state certification program and were not confirmed here. Check your state program for current fees.

After you are certified, your state program sets renewal and continuing education requirements; check it for current rules.

Start with the heaviest areas of the content outline: Equipment Evaluation, Maintenance, and/or Operation (39.0%); Treatment Process Evaluation and Adjustment (38.0%); Security, Safety, and Administrative Procedures (13.0%). Then work through the remaining areas, practise jurisdiction-specific rules separately from the general content, and finish with timed full-length practice runs of 100 questions in one sitting.

Content outlines, fees and passing standards change; this guide follows the materials listed under Verification as of October 2026. Check the licensing authority and test administrator before you register.