The water treatment study center
Every module and guide for the water treatment exam, organized by the exam's own duty list and weights. Free, no signup.
Closed book. About 100 questions. Formula sheet provided. Scaled score of 70 to pass.
Class I is the entry-level license, whatever your state calls the grade. Weights below are the 2025 WPI/ABC Need-to-Know Criteria, Class I.
Start here
A comfortable runway is six weeks: a duty or two a week, math in week five, timed tests in week six.
What's on the exam, and what covers it
Five duties, weighted by the exam itself. The minutes are real read times; a first pass through everything below is about an hour, and passing takes running it more than once. Weights from the 2025 WPI/ABC Need-to-Know Criteria, Class I.
Treatment process
- Coagulation and flocculation · 3 min
- Sedimentation and clarification · 3 min
- Filtration · 3 min
- Disinfection and CT · 3 min
- Residuals and corrosion control · 2 min
- Membranes and alternative processes · 2 min, weighted heaviest at Class III and IV
- Process control · 5 min
In the order the water moves through the plant.
Source water characteristics
- Source water and intake · 3 min
- Microbiology and public health · 4 min
Security, safety and admin
- Operator safety · 3 min
- Records and reporting · 3 min
- Regulations and compliance · 4 min
of every duty above is calculations
- Water treatment math · 2 min
- Operator math fundamentals · 5 min
The Class I split runs about 40/60 recall to application: know the facts, then practice applying them.
Drill the math
About 10% of the questions are calculations, and they are the ones people leave blank. Most are five formula families: dosage, detention time, flow, the 8.34 conversion, and area and volume. Learn the steps, then make the calculator show its work until you do not need it.
Check your readiness
Test yourself before the state does
The practice bank is the fastest way to find your weak duties. Use it cold on day one, then timed in your last week.
Practice tests
Includes the water treatment bank: original questions, every answer backed by a source, weak topics highlighted. Practice or timed.
Take a practice testOperator calculator
8.34 lb/gal is the number the exam never stops using. The calculator runs dosage, detention time and loading with worked steps, not just an answer.
Open the operator calculatorFormula sheets
Your water treatment formulas on one page, grouped the way the exam groups them, next to the other three disciplines.
Open the formula sheetsThen check your state's rules
The exam is a national standard; the license comes from your state. Find your state on the operator door's map for grades, applications and renewal. Then compare across states: what certification costs, whether your license transfers, and the CEUs renewal takes.
The other exam tracks
Water distribution · Wastewater treatment · Wastewater collection
Each is built the same way from its own exam's weights. Or head back to the operator door to pick your track and find your state. A free resource from Ziptility. We make software for small water systems.