Water Treatment Class I Practice Test (ABC/WPI)
Original Class I questions written to WPI’s 2025 Need-to-Know Criteria, every option explained.
Which form of chlorine is a liquid sold in drums or bulk at about 10 to 15 percent available chlorine?
180 original Water Treatment Class I questions with explanations · 100-question practice exam · 5 parts
Water Treatment Class I exam format
Water Professionals International (WPI, formerly the Association of Boards of Certification, ABC) writes the standardized water treatment operator exams that many state certification programs use. The 2025 Class I exam has 100 scored questions in 5 content areas; 10% are calculations. Your state sets eligibility, fees, the time limit and the passing score.
- Questions
- 100 scored, plus up to 10 unscored pretest questions mixed in
- Content (2025 Need-to-Know)
- Treatment Process 31, Laboratory Analysis 16, Equipment Operation and Maintenance 26, Source Water Characteristics 15, Security, Safety, and Administrative Procedures 12
- Calculations
- 10% of the exam; WPI provides its Formula/Conversion Table, and items give US and metric units
- Rules of the exam
- Closed book. Bring photo ID and a non-programmable calculator
- Time, fee and passing score
- Set by your state certification program, not by WPI
- Results
- Reported by your certifying authority; WPI does not give results to candidates
- Language
- The 2025 Class I and II exams are also available in Spanish
- Which version
- This page follows the 2025 standardized exam. Some programs still use older editions or custom exams; ask your certifying authority
What’s on the Water Treatment Class I exam
The content areas and question counts below are the exam owner’s. Our practice exam uses the same counts; each row links to the free topic drills that practice it.
| Content area | What it covers | Questions (official) | Drill |
|---|---|---|---|
| Treatment Process | Coagulation through filtration, disinfection, corrosion control, fluoridation and other processes | 31 | Coagulation and filtration drillDisinfection drillCorrosion and chemistry drill |
| Laboratory Analysis | Sampling and lab tests | 16 | Water lab drill |
| Equipment Operation and Maintenance | Pumps, motors, feeders, meters and instruments | 26 | Pumps and equipment drill |
| Source Water Characteristics | Wells, surface water and source quality | 15 | Source water drill |
| Security, Safety, and Administrative Procedures | Safety, security, records and regulations | 12 | Safety drillManagement drillRegulations drill |
How to take the Water Treatment Class I exam
- Check with your state certifying authority that it uses the WPI standardized exam and which edition.
- Meet your state’s education and experience rules and apply to the state program.
- Study the content areas in WPI’s Need-to-Know Criteria and the formula table.
- Sit the exam under your state’s rules; your state reports your result.
Common questions
How many questions are on the Water Treatment Class I exam?
100 scored questions plus up to 10 unscored pretest questions. WPI's 2025 Need-to-Know Criteria split them: Treatment Process 31, Laboratory Analysis 16, Equipment Operation and Maintenance 26, Source Water Characteristics 15, Security, Safety, and Administrative Procedures 12.
What is the passing score?
WPI does not set one for candidates; each state certification program sets its passing score, time limit and fees. Our practice exam shows your score in each content area.
Is ABC the same as WPI?
Yes. The Association of Boards of Certification (ABC) is now Water Professionals International (WPI), and ABC Testing is its testing service.
Do I get a formula sheet?
Yes. WPI provides its Formula/Conversion Table with the exam. 10% of the Class I questions are calculations.
Are these real WPI questions?
No. WPI exam questions are copyrighted and confidential. These are original practice questions written to the published Need-to-Know Criteria, with an explanation for every option.
Ready for exam day?
100 questions in the official content counts, with a score for every area and an explanation for every option.
Or start with a free ten-question drillMore ABC/WPI exam practice
One water operator pass covers every practice exam on the site.
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- Water Distribution Class I Practice Test (ABC/WPI)
- Water Distribution Class II Practice Test (ABC/WPI)
- Wastewater Treatment Class I Practice Test (ABC/WPI)
- Wastewater Treatment Class II Practice Test (ABC/WPI)
- Wastewater Collection Class I Practice Test (ABC/WPI)
- Wastewater Collection Class II Practice Test (ABC/WPI)
- All water operator exams and topics
Content-area counts and exam rules checked November 2026 on gowpi.org (2025 Need-to-Know Criteria): WPI: 2025 Need-to-Know Criteria · WPI Water Treatment Operator Class I Need-to-Know Criteria (PDF) · WPI: Information for examinees.
Game Assessment Prep is an independent practice site, not affiliated with or endorsed by Water Professionals International (WPI, formerly ABC), the California State Water Resources Control Board or the Texas Commission on Environmental Quality. Every question is original; none is taken from a certification exam, an official study guide or another prep provider.