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The wastewater treatment study center

Every module and guide for the wastewater 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

1Take a practice test cold. It shows you your weak duties before you spend a week rereading.
2Study the map below: heaviest duty first, your weakest topics first.
3Drill the math until the steps are boring, then practice again, timed.

A comfortable runway is six weeks: a duty or two a week, math in week five, timed tests in week six.

Take the practice test

What's on the exam, and what covers it

Four duties, weighted by the exam itself. The minutes are real read times; a first pass through everything below is close to two hours, and passing takes running it more than once. Weights from the 2025 WPI/ABC Need-to-Know Criteria, Class I.

39%

Equipment evaluation, maintenance and operation

 

The heaviest duty on this exam is the machinery, not the biology.

38%

Treatment process evaluation and adjustment

 

In the order the flow moves, from the headworks to biosolids.

13%

Security, safety and admin

 
10%

Laboratory

 
~10%

of every duty above is calculations

The Class I split runs about 31/69 recall to application, the most application-heavy of the four exams: practice beats rereading here.

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.

Wastewater treatment math

The plant calculations worked in steps: loading, detention time, MLSS and sludge age.

Operator math fundamentals

The base layer: units, conversions, and the 8.34 relationship everything else stands on.

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.

Start here

Practice tests

Includes the wastewater treatment bank: original questions, every answer backed by a source, weak topics highlighted. Practice or timed.

Take a practice test
8.34

Operator calculator

8.34 lb/gal is the number the exam never stops using. The calculator runs loading, detention time and dosage with worked steps, not just an answer.

Open the operator calculator
Print it

Formula sheets

Your wastewater treatment formulas on one page, grouped the way the exam groups them, next to the other three disciplines.

Open the formula sheets

Then 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 treatment · Water distribution · 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.