Chlorination and Disinfection Practice Questions

Disinfection is 15 to 20 questions on every California distribution exam and part of treatment processes on the T exams. Practice the chemistry and the safety.

Take the California D2 practice exam

100 questions in the official content counts, with a score for every area and an explanation for every option.

Or try the free disinfection drill
  • 36 original disinfection questions, every option explained
  • Tested on 16 of our 25 practice exams
Free sample · Question 1 of 3Disinfection

How do operators find a small chlorine gas leak at a cylinder valve?

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What our disinfection questions cover

  • Gas chlorine, sodium hypochlorite and calcium hypochlorite
  • HOCl and OCl−, pH, breakpoint curves, free and combined residuals
  • CT, T10 and baffling factors; Giardia, virus and Cryptosporidium credit
  • Chloramines, nitrification, UV and ozone; THMs, HAA5, bromate and chlorite
  • Chlorine leaks and first aid; disinfecting mains, tanks and wells
Line drawing of a wall-mounted gas chlorinator with a rotameter and vacuum regulator on an upright chlorine cylinder chained to the wall, a breathing apparatus and a chlorine test colorimeter

This list is our own summary, written for practice. The exam owners publish their outlines: California’s Expected Range of Knowledge, TCEQ’s Need-to-Know Criteria and WPI’s Need-to-Know Criteria.

Drill disinfection, then sit a full practice exam

Take the California D2 practice exam

100 questions in the official content counts, with a score for every area and an explanation for every option.

Or try the free disinfection drill

Ideas the questions test most

  1. Dose = demand + residual.
  2. Lower pH favors HOCl, the stronger disinfectant.
  3. MRDL: chlorine and chloramines 4.0 mg/L; chlorine dioxide 0.8 mg/L.
  4. AWWA C651 mains, C652 storage, C654 wells.

Start the free disinfection drill · California D2 practice test · California T1 practice test · California T2 practice test · California T3 practice test · California T4 practice test · California D1 practice test

Common questions

What is CT?

Disinfectant residual (mg/L) multiplied by contact time (minutes), usually T10 from a tracer study or baffling factor. Required CT rises in cold water and at higher pH.

How is a new main disinfected?

AWWA C651: flush, chlorinate (for example 25 mg/L held 24 hours with at least 10 mg/L remaining), flush the strong water, then pass bacteriological samples before service.

Take the California D2 practice exam

100 questions in the official content counts, with a score for every area and an explanation for every option.

Or try the free disinfection drill

More operator topics

Outlines used for these questions: Expected Range of Knowledge, Drinking Water Treatment Exam (rev. 4/2020, PDF) · Expected Range of Knowledge, Drinking Water Distribution Exam (rev. 4/2020, PDF) · TCEQ: Need-to-Know Criteria for public water system operators · TCEQ: What applicants for wastewater licenses need to know · WPI: 2025 Need-to-Know Criteria.

Game Assessment Prep is an independent practice site, not affiliated with or endorsed by Water Professionals International (WPI, formerly ABC), the California State Water Resources Control Board or the Texas Commission on Environmental Quality. Every question is original; none is taken from a certification exam, an official study guide or another prep provider.