California D4 Water Distribution Practice Test
Original D4 questions written to the State Water Board’s Expected Range of Knowledge, every option explained.
Which treatment is commonly applied to a reservoir to control algae, under the appropriate permit?
345 original California D4 questions with explanations · 100-question practice exam · 6 parts
California D4 exam format
California certifies drinking water distribution operators at grades D1 to D5. The D4 exam has 100 questions in six content categories, with counts set for each grade in the Board's Expected Range of Knowledge, taken on computer at Prometric test centers year-round.
- Questions
- 100: Disinfection 15, Design/Hydraulics 10, Equipment/Maintenance/Inspections 20, Regulations/Management/Safety 35, Mains and Piping 5, Water Quality/Source 15
- Where
- Computer-based at Prometric test centers in California, year-round
- Exam fee
- $162; re-exam $119 (fee schedule effective 8/31/2026)
- Time and passing score
- The Board does not publish the time limit or the passing score for the D exams
- Results
- Drinking water results are available right after the exam
- Recent pass rate
- 56% of 177 examinees, January to June 2026 (State Water Board)
- To take the exam
- A valid D3 certificate and three such courses, at least two in water supply principles
- Certificate
- Pass within three years before applying, plus the grade’s operator experience. Certificates are valid three years; renewal needs 36 contact hours
What’s on the California D4 exam
The content areas and question counts below are the exam owner’s. Our practice exam uses the same counts; each row links to the free topic drills that practice it.
| Content area | What it covers | Questions (official) | Drill |
|---|---|---|---|
| Disinfection | Main, well and reservoir disinfection, chlorine chemistry, chloramination and byproducts | 15 | Disinfection drill |
| Distribution System Design / Hydraulics | Layout, storage, demand, pressure, head loss, water hammer, cavitation, cross-connections and backflow | 10 | Hydraulics drillBackflow drill |
| Equipment Operation / Maintenance / Inspections | Valves, hydrants, meters, pumps and motors, feeders, generators, SCADA and inspections | 20 | Mains and valves drillPumps and equipment drill |
| Drinking Water Regulations / Management / Safety | SDWA rules, MCLs, sampling, public notice, planning, budgets, safety and emergency response | 35 | Regulations drillManagement drillSafety drill |
| Water Mains and Piping | Pipe materials, installation, services, repairs, flushing and corrosion | 5 | Mains and valves drill |
| Water Quality / Water Source | Sampling and lab results, source water and wells | 15 | Water lab drillSource water drill |
How to take the California D4 exam
- Check the D4 requirements and apply to the State Water Board with the exam fee ($162).
- Once approved, schedule the exam with Prometric at a California test center.
- Sit the 100-question exam with the on-screen calculator, scratch paper and the Board’s formula sheet.
- Apply for the D4 certificate within three years of passing.
Common questions
How many questions are on the California D4 exam?
100, in six categories: Disinfection 15, Distribution System Design/Hydraulics 10, Equipment Operation/Maintenance/Inspections 20, Drinking Water Regulations/Management/Safety 35, Water Mains and Piping 5 and Water Quality/Water Source 15.
What is the passing score for the D4 exam?
The State Water Board does not publish a passing score or time limit for the distribution exams. Our practice exam reports your score in each category.
What is the D4 pass rate?
56% of 177 examinees passed D4 from January to June 2026, according to the Board's published results.
What do I need to take the D4 exam?
A valid D3 certificate and three such courses, at least two in water supply principles.
Are these the real exam questions?
No. The Board keeps exam questions confidential. These are original questions written to its published Expected Range of Knowledge, with an explanation for every option.
Ready for exam day?
100 questions in the official content counts, with a score for every area and an explanation for every option.
Or start with a free ten-question drillMore California exam practice
One water operator pass covers every practice exam on the site.
- California T1 Water Treatment Practice Test
- California T2 Water Treatment Practice Test
- California T3 Water Treatment Practice Test
- California T4 Water Treatment Practice Test
- California D1 Water Distribution Practice Test
- California D2 Water Distribution Practice Test
- California D3 Water Distribution Practice Test
- California Wastewater Grade I Practice Test
- California Wastewater Grade II Practice Test
- All water operator exams and topics
Exam format, content counts, fees and pass rates checked November 2026 on waterboards.ca.gov: State Water Board: Drinking Water Treatment and Distribution Operators · Expected Range of Knowledge, Drinking Water Distribution Exam (rev. 4/2020, PDF) · Drinking Water Operator Certification fee schedule (effective 8/31/2026, PDF) · Distribution operator minimum qualifications (rev. 11/2024, PDF) · Water Distribution exam results (PDF) · Operator Certification Computer-Based Testing FAQs (rev. 2/2023, PDF) · Distribution and Water Treatment Operator Certification Guidance (rev. 6/2024, PDF).
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.