If you are not sure which NICET WBSIT level you actually need, here is the short version.
Level I is for technicians doing limited job tasks under direct supervision. The exam is 115 questions in 125 minutes, and it focuses on knowing the system in front of you: inspecting and testing existing water based systems, spotting damage or deficiencies, and following the frequencies in NFPA 25.
Level II is for technicians doing routine inspection and testing under limited supervision, meaning less hand holding and more judgment calls. The exam is bigger, 168 questions in 185 minutes, and it goes further into diagnosing problems and understanding why a system is deficient, not just recognizing that it is.
Level III is for technicians who can work independently on complex inspection and testing jobs. The exam is 145 questions in 155 minutes and leans on real judgment: unusual system configurations, code interpretation, and situations that do not have one obvious answer.
In practice, most people move through these in order, and the jump from Level I to Level II is usually where people are most surprised by how much more the exam expects from them. Studying with practice exams built at the right level, not just more of the same Level I material, makes that jump a lot less rough.
Ignite Prep has full length practice exams for all three levels. See all levels.