Regulations, management and safety jump to 35 questions; hydraulic gradient, pumping cost and well abandonment first appear.
For the operators who keep treated water moving through the pipes, pumps, valves and storage between the plant and the customer.
Start studying D4| Content area | % of the exam | |
|---|---|---|
| Disinfection | 15 | |
| Distribution System Design / Hydraulics | 10 | |
| Equipment Operation / Maintenance / Inspections | 20 | |
| Regulations / Management / Safety | 35 | |
| Water Mains and Piping | 5 | |
| Water Quality / Water Source | 15 |
56% of examinees passed (189 of 339) from July 1, 2025 to June 30, 2026. Source: SWRCB Drinking Water Operator Certification Program, Water Distribution Exam Results (through 6/30/2026). The agency updates these tables every six months.
Pumping cost · an original practice item written only from publicly available sources, not a real exam question
A booster pump delivers 1,500 gallons per minute (gpm) against 150 ft of total dynamic head for 12 hours a day. The wire-to-water efficiency is 75% and power costs $0.20 per kWh. What is the daily energy cost?
A. $136
Water horsepower = 1,500 × 150 ÷ 3,960 = 56.8 hp. Input = 56.8 ÷ 0.75 = 75.8 hp × 0.746 = 56.5 kW. Daily cost = 56.5 kW × 12 h × $0.20 = $136. $182 prices horsepower as if it were kilowatts (75.8 × 12 × $0.20), $203 ignores the efficiency and runs the pump 24 hours, and $271 includes the efficiency but runs the pump 24 hours.
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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.