High school diploma or General Educational Development (GED).
One specialized course in water supply principles.
The high school diploma or GED requirement can also be met by completing the State Water Board Basic Small Water Systems Operations course, or by one year operating a facility that required an understanding of chemical feeds, hydraulics and pumps (treatment) or piping, pumps, valves and storage tanks (distribution).
To be certified at D2
Pass the D2 exam within three years before applying. No experience requirement.
A specialized course means one course of at least 36 contact hours, 3.6 continuing education units (CEU), or 3 college semester units, from an accredited institution or an International Association for Continuing Education and Training (IACET) accredited or authorized provider.
The passed examination must be within three years before the certification application.
The Expected Range of Knowledge (ERK) lists 262 objectives tested at D2, 104 of them new at this grade.
Disinfection: new main · an original practice item written only from publicly available sources, not a real exam question
A new 8-inch main 2,500 ft long is to be disinfected at 25 mg/L. How many pounds of pure (100% available) chlorine are needed?
0.18 lb
1.36 lb
2.09 lb
5.44 lb
Answer and working
B. 1.36 lb
Diameter = 8 ÷ 12 = 0.667 ft. Volume = 0.785 × 0.667 ft × 0.667 ft × 2,500 ft = 872 ft³ × 7.48 = 6,524 gal, or 0.006524 million gallons (MG). Pounds = 0.006524 × 25 × 8.34 = 1.36 lb. 0.18 skips the cubic-foot-to-gallon step; 2.09 is the weight of 65% calcium hypochlorite needed, not of pure chlorine; 5.44 treats the 8-inch diameter as the radius.
D2 questions answered
What do I need to sit the D2 distribution exam?
High school diploma or GED. One specialized course in water supply principles. The high school diploma or GED requirement can also be met by completing the State Water Board Basic Small Water Systems Operations course, or by one year operating a facility that required an understanding of chemical feeds, hydraulics and pumps (treatment) or piping, pumps, valves and storage tanks (distribution).
How is the D2 exam weighted?
Disinfection: 20; Distribution System Design / Hydraulics: 20; Equipment Operation / Maintenance / Inspections: 20; Regulations / Management / Safety: 10; Water Mains and Piping: 20; Water Quality / Water Source: 10 (percent of the exam).
What is the recent D2 pass rate?
67%: 1,266 of 1,898 examinees passed from July 1, 2025 to June 30, 2026, summed from the agency's two half-year results tables.
What this exam covers
Hydraulics & Pumping
Storage
Water Quality in Distribution
Main Disinfection & Flushing
Cross-Connection Control
Regulations (LCR / CCCPH / Title 22)
Water Mains & Piping
Operations & Maintenance
How to study for it here
Practice quizzes — filter to any topic above and work through it with explanations.
Flashcards — spaced repetition over terms, formulas and regulations.
Mock exam — a timed run at this grade.
Official formula sheet — a link to the sheet the certifying body publishes for this exam, where it publishes one, so you study from the real thing.
Free, no account, and progress stays in your browser.
Topic coverage follows Expected Range of Knowledge for Drinking Water Distribution Exam (SWRCB Division of Drinking Water, rev. 4/2020).
Practice questions are written only from publicly available sources
(that outline and the regulations and references it cites); they are
not real exam questions, which are confidential.
Check current application requirements, fees and exam dates on the
certifying body's own page: official certification page.
Questions, flashcards, and explanations are AI-written from publicly available sources only: the exam content outlines and candidate materials each certifying body publishes without restriction, and the regulations and technical references they cite. No confidential material is used, including actual exam questions, recollections of any exam sat by the author, or any handbook or document released under a confidentiality agreement. Content is then put through repeated review — regulatory values checked against primary sources, every calculation recomputed, and errors corrected — plus spot checks by the author, who holds California water operator certifications and a California civil engineering licence. Those spot checks are sampling, not a professional review: nothing here is stamped, sealed, or offered as engineering advice, and not every item has been individually verified, so mistakes can still slip through.