Studying for a Wisconsin water or wastewater operator exam? You're in the right place. Pick your discipline below: each tab has the certification levels, how Wisconsin names them, and the practice tests that match.
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Choose your certification
How Wisconsin classifies drinking-water operators
Wisconsin does not build a ladder. Where most states ask which grade you hold, Wisconsin asks which processes run at your plant, and you certify in a subclass for each one.
Full breakdown in the FAQ below.
Choose your Wisconsin subclass
Source water subclasses (G and S)
Treatment process subclasses (I, L, Z and V)
Small water systems (OTM and NN)
Wisconsin wastewater practice tests
Wisconsin wastewater certification is built on processes rather than plant size. Plants are rated Basic or Advanced, and then assigned subclasses matching the processes they actually run. There are thirteen subclasses in eight categories. Biological treatment splits into A1 suspended growth, A2 attached growth, A3 recirculating media filters, A4 ponds and lagoons, and A5 anaerobic treatment of high strength liquid waste. Then B is solids separation, C is biological solids handling and reuse, D is disinfection, L is laboratory, N is total nitrogen, P is total phosphorus, SS is sanitary sewage collection, and U covers unique treatment systems. Each plant designates an operator-in-charge certified at the plant class level and in every subclass the plant uses. To get certified you pass the Basic General Wastewater exam plus at least one subclass exam, and the only two subclasses exempt from the General exam are SS and U. The levels are Operator-in-Training, which takes the exams; Basic, which adds one year of subclass-specific experience; and Advanced, which takes ten advanced points and a separate application. A year of experience means full-time employment at a plant or 1,000 cumulative hours over at least twelve months for part-timers. Exams need 75% to pass. One trap to watch: subclass D means Disinfection in the wastewater program and Distribution in the waterworks program, so an operator holding both certifications holds two very different subclass Ds.
General exam (required before almost every subclass)
Biological treatment subclasses (A1 through A5)
Wisconsin Subclass A1, Suspended Growth Practice Test
Subclass A1 is suspended growth, meaning activated sludge and its variants. MLSS, F/M, SRT, settleability, return and waste rates, and the process troubleshooting that fills an operator's day at a conventional plant.
DNR · A2 · trickling filters and RBCsWisconsin Subclass A2, Attached Growth Practice Test
Subclass A2 is attached growth, covering trickling filters, rotating biological contactors and biotowers. Worth pairing with subclass A3, recirculating media filters, which is a separate Wisconsin subclass working closely related media and recirculation principles.
Solids, disinfection and laboratory subclasses (B, C, D and L)
Wisconsin Subclass C, Solids Handling Practice Test
Subclass C is biological solids and sludge handling, processing and reuse, covering aerobic and anaerobic digestion, thickening, dewatering and land application. Land application matters in Wisconsin, where biosolids often go to farmland under a management plan.
DNR · Subclass D · chlorine, UV, ozoneWisconsin Subclass D, Disinfection Practice Test
Subclass D on the wastewater side is disinfection by chlorination, ultraviolet radiation or ozone. Note that D means something completely different here than on the water side, where Subclass D is Distribution. Dose, contact time, residual, dechlorination and UV transmittance.
Nutrient removal subclasses (N and P)
Wisconsin's distribution certification is Subclass D, one of the seven waterworks subclasses under NR 114. It is not a separate ladder and it has no grades of its own beyond the statewide Grade T and Grade 1. Subclass D applies to any waterworks containing a distribution system, so nearly every municipal operator in the state carries it alongside a source subclass. Grade T takes only the exam. Grade 1 adds one year of satisfactory experience, counted as full-time work or 1,000 cumulative hours over at least twelve months. Exams need 75% to pass. One useful side effect of holding Subclass D is that it also qualifies you to operate small OTM and NN water systems without sitting their general operation exam, which is the same waiver that Subclass G and Subclass S carry.
Wisconsin Subclass D, Distribution Practice Test
Subclass D covers any waterworks containing a distribution system. Mains, valves, hydrants, storage, pressure zones, flushing, main disinfection and distribution water quality. Holding it also waives the general operation exam for small OTM and NN systems.
DNR · Subclass D topicDistribution Fundamentals, Wisconsin Grade T Support
Mains, valves, hydrants, storage and safety basics. The ground to cover before sitting the Subclass D exam for a Grade T certificate.
DNR · Subclass D topicDistribution Operations, Wisconsin Subclass D Support
Main disinfection, flushing, sampling, cross-connection control and pressure management.
DNR · Subclass D topicDistribution Hydraulics, Wisconsin Subclass D Support
Pumping, storage turnover and system hydraulics, plus the water quality problems that show up in long or low-turnover Wisconsin mains.
Wisconsin does certify collection system operators. Under NR 114 the credential is subclass SS, Sanitary Sewage Collection System, one of the thirteen wastewater subclasses. SS is unusual in one respect worth knowing before you apply. Most Wisconsin wastewater subclasses require you to pass the Basic General Wastewater exam plus the subclass exam, but the Collection System certification is exempt from the General exam, as is the Special U subclass. So SS can be held on its own without the general wastewater material behind it. The levels work the same as the rest of the wastewater program. Operator-in-Training takes the exam, Basic adds one year of subclass-specific experience, and Advanced takes ten advanced points and a separate application. The four practice tests below work the SS material at increasing depth.
Wisconsin Subclass SS, Collection Fundamentals Practice Test
Pipe, manholes, cleaning, safety and confined space awareness. Foundation material for the Wisconsin subclass SS certification, which does not require the Basic General Wastewater exam.
DNR · Subclass SS · operationsWisconsin Subclass SS, Collection Operations Practice Test
Lift station operation, inspection and televising, infiltration and inflow, and sanitary sewer overflow response.
DNR · Subclass SS · advancedWisconsin Subclass SS, Advanced Collection Practice Test
Force mains, pump station hydraulics and corrosion control. Useful ground if you are working toward the Advanced level, which takes ten advanced points.
DNR · Subclass SS · large systemsWisconsin Subclass SS, Large System Collection Practice Test
System-wide rehabilitation planning, capacity assessment and regulatory compliance across a large collection network.
About the Wisconsin operator exams
Operator certification in Wisconsin covers several disciplines, drinking water, wastewater, distribution, and collections, which may be handled by the same agency or by separate programs (drinking water is administered by Wisconsin DNR, Operator Certification Program, governed by Wisconsin Administrative Code Chapter NR 114). The exact certification structure, exam format, levels, and continuing-education requirements vary by discipline and change over time, so always confirm the current scope and eligibility directly with the certifying agency. Our practice content focuses on the underlying technical material: the same operating principles, math, regulations, and process knowledge that show up on water and wastewater operator exams nationwide.
Frequently asked questions
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Disclaimer: WaterOperatorPracticeTest.com is an independent study aid. We are not affiliated with Wisconsin DNR, Operator Certification Program, governed by Wisconsin Administrative Code Chapter NR 114 or any state primacy agency. Always confirm current exam requirements with your state's certification body.