Median Pay by Area
- St. Louis, MO-IL
- $57,850 a year
- Kansas City, MO-KS
- $52,770 a year
- Columbia
- $50,270 a year
- Springfield
- $49,270 a year
- Jefferson City
- $48,550 a year
- Central Missouri nonmetropolitan area
- $47,740 a year
Missouri wastewater operators
The steps from no certificate to a Missouri wastewater treatment operator certificate, how to qualify for and pass the exam, how to keep your certificate active and what operators earn. Every requirement links to the Missouri Department of Natural Resources (DNR) Operator Certification Unit or its rule, 10 CSR 20-9.
DNR makes the final eligibility determination. Check with DNR before you apply.
Why it matters
Missouri requires certified operators at wastewater treatment systems that serve a population equivalent of more than 200 and are owned or operated by or for cities, public sewer districts, counties, public water supply districts, private sewer companies regulated by the Public Service Commission, or state or federal agencies. DNR can also require certified operators at other systems to protect Missouri's waters.
Every operator at these systems needs at least a Level D certificate. New employees who are not yet certified cannot make process control decisions and must be directly supervised by a certified operator or the chief operator.
The chief operator, the person in direct responsible charge, must hold the level DNR sets for the facility. The owner must tell DNR within 15 days when the chief operator changes or leaves.
You must be at least 18 years old to be certified.
Missouri has four wastewater treatment certificate levels: D, C, B and A. Level D is the lowest and Level A the highest.
DNR scores each treatment plant with a point system based on its size, where it discharges, its treatment processes, solids handling, disinfection and lab work. Plants with 25 points or fewer need a Level D chief operator, 26 to 50 points Level C, 51 to 70 points Level B, and 71 points or more Level A.
The exam application lists Wastewater Treatment levels D to A and no separate wastewater collection exam. Work on a wastewater collection system counts toward a treatment certificate only as equivalent experience.
Step 1
Each level needs a set amount of operating experience. Actual experience means making or acting on day-to-day process control decisions at a wastewater treatment system, not textbook study or watching a supervisor.
Good experience includes sample collection, routine operational monitoring, reading test results, calculating chemical doses and adjusting feeders and aeration, flow and pumping adjustments, disinfection and completing operating reports.
You also need one of these: a high school diploma, a GED, a special DNR-approved training course, or six months of hands-on experience on top of the experience your level needs.
Step 2
Part of the experience for each level can be equivalent experience. Running a drinking water treatment plant or a wastewater collection system counts year for year.
Education counts too: an approved one-year water or wastewater technology certificate counts as 1 year, a two-year associate degree in an allied field such as environmental science, biology or chemistry as 1½ years, and a four-year degree in an allied field as 2 years.
College courses in biological or environmental sciences with a grade of C or better count as 1 month per 3 semester hours, up to six months. Approved multi-week entry-level, advanced or correspondence courses count as ½ year each, up to 1 year. Other related training or work is judged case by case, up to six months.
DNR's training list marks courses worth six months of equivalent experience in the certificate area.
Step 3
Mail the Application for Examination (MO 780-1089) to DNR and allow 30 days for processing. Faxes and emails are not accepted, and incomplete applications are returned. Use a separate application for each exam.
The wastewater exam fee is $45 for a first application. It covers the exam and the certificate when you qualify. Pay by check or money order, a DNR wastewater voucher, or card or eCheck online, adding the confirmation number to the application.
List all of your water, wastewater and collection experience, with the facility permit number for wastewater work, and attach a copy of any college transcript. The application also asks for your Social Security number, and your name must match your photo ID.
Wastewater facilities with domestic discharges under 1.0 million gallons a day that must have a certified operator can get DNR training vouchers. DNR mails voucher packets to eligible systems each January, and they expire December 31.
Step 4
Once DNR processes your application, PSI emails you instructions to create an account and schedule your exam. You can take it at a PSI test center or online at home with a live remote proctor.
You have one year from your application date to take the exam. To reschedule, give at least 48 hours' notice; otherwise you must send a new application and fee.
If you plan to test remotely, run PSI's compatibility check first. DNR suggests a personal computer, because work computers often block the secure exam browser.
Step 5
After you pass, DNR reviews the education and experience on your application. If you qualify, it issues a certificate valid for three years.
You can take the exam before you have all the experience. If you pass without enough experience, you have 18 months from the exam to gain it; after that you must test again.
Tell DNR when your name, address or employer changes.
Step 6
Renew every three years. Before your certificate expires, complete at least 30 hours of DNR-approved renewal training, then send the renewal application and the $45 renewal fee.
Only DNR-approved training counts. Credit is based on actual contact time, and one CEU from a qualifying provider counts as 10 hours. Extra hours do not carry over to the next renewal period.
DNR sends a renewal notice about 60 days before your certificate expires, but renewing is your responsibility even if it never arrives. You can check your training hours, update your contact details and renew online in DNR's Operator Certification Database.
If your hours were done on time, you have 60 days after expiration to renew, with a late fee of $10 a month up to $20. There is no grace period for the training hours. A certificate not renewed within 60 days lapses, and you must pass the exam again.
Exam day
The exams are computer-based and multiple choice. Each wastewater test description lists 100 multiple-choice questions. You pass with a score of 70% or higher.
Questions cover Missouri wastewater regulations, general wastewater knowledge, water quality, applied math, chemistry, wastewater lab tests, hydraulics, pumps and operation. DNR's test description for each level breaks the exam down by topic and lists study resources.
The math formula sheet is on screen under the resource tab during the exam. At a test center you get scratch paper and a pencil and may bring your own non-programmable calculator. Remote test takers may use two sheets of blank scratch paper and a pencil, or a whiteboard and dry erase marker, and a non-programmable calculator.
Starting January 1, 2027, DNR switches to WPI standardized exams. DNR matches Level D to WPI's Wastewater Treatment Operator Class 1 criteria, Level C to Class 2, Level B to Class 3 and Level A to Class 4. Each new exam has 100 scored questions plus 10 unscored sample questions, and fuller math formula sheets.
If you fail, wait at least 60 days and send a new application with the $20 retake fee for the same type and level. After three fails at the same level, you must finish a DNR-approved multi-day wastewater training course within the previous 12 months before testing again.
Missouri moves to WPI standardized exams on January 1, 2027. Operator Master's free practice questions, timed practice exam and math help are built on the WPI exam format and the WPI formula table, so they fit the new exams most closely. Until then, use DNR's test descriptions for your level as your main guide to what the Missouri exam covers. Operator Master is an independent study tool, not the official exam.
Pay
The median pay for water and wastewater treatment plant and system operators in Missouri was $49,940 a year ($24.01 an hour) in 2025, compared with $60,020 nationally. One in ten earned $38,600 or less, and one in ten earned $64,930 or more.
These federal figures cover drinking water and wastewater operators together, at every level. Pay for a new operator is usually nearer the low end.
Moving up
Every level also needs a high school diploma, a GED, a DNR-approved training course or six extra months of experience, and you must be at least 18. Equivalent experience comes from drinking water or collection work, education and approved courses.
From another state
DNR can issue a Missouri certificate without an exam if you hold a valid certificate earned by exam elsewhere under requirements at least as strict as Missouri's, and you have worked at a wastewater treatment system where it was issued.
You must work for a Missouri wastewater treatment system and apply within 180 days of starting that job. If you are not yet employed in Missouri, DNR can issue a letter of intent valid for 180 days.
Send the Application for Reciprocity (MO 780-1091) with a copy of your current certificate and the $40 application fee; DNR invoices a $25 certificate fee before issuing the certificate. Your Missouri level is based on the requirements for the level you hold in your home state.