D1 Water Distribution Practice Test

Our own questions on California's D1 and D2 outlines, each naming the rule or page behind the answer.

Exam grade

Chlorine is dosed at 2.5 mg/L and the residual after contact is 0.6 mg/L. What is the chlorine demand?

Pick an answer, then press Check answer. Then you see Correct or Not quite, with the reason. Keys: A to D pick, Enter checks.

Print covers the next 25 questions. Share this set copies a link to the same questions in the same order.

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Unofficial practice questions, not affiliated with the California State Water Resources Control Board. Bank checked October 11, 2026.

The real exams, as the State Water Board describes them

Questions
100 at each grade, by the count in the state outline.
D1 by category
Disinfection 15, Distribution System Design and Hydraulics 20, Equipment Operation, Maintenance and Inspections 20, Regulations, Management and Safety 15, Water
D2 by category
Disinfection 20, Distribution System Design and Hydraulics 20, Equipment Operation, Maintenance and Inspections 20, Regulations, Management and Safety 10, Water
How it is given
On a computer at test centers across the state, all year. A calculator is built into the test screen, and a dry erase board or scratch paper is provided.
Formula sheet
The state's Equivalents and Formula sheet for drinking water exams is provided at the test.
Time and pass mark
The state pages this site read give neither. Ask the Office of Operator Certification.

Checked October 11, 2026 against the State Water Board's Expected Range of Knowledge for Drinking Water Distribution Exam (rev. 4/2020) and its Computer Based Testing FAQs. Rules change, so confirm with the agency itself before your test.

The State Water Board's operator certification page

Next step California T1 and T2 treatment practiceWater operator math practice test

All 46 questions

Disinfection 7

  • A chlorine solution is injected into a newly laid main to disinfect it. About what concentration should it reach in the pipe? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2, Basic Water Main Installation, pages 2-6 and 2-7
  • A repaired water main has been disinfected and sampled. What must the samples show before a new main goes into service? California Code of Regulations, Title 22, section 64580
  • A storage tank holding 50,000 gallons needs a 10 mg/L chlorine dose. The crew has 65 percent calcium hypochlorite. How many pounds go in? Worked arithmetic; formula on the California State Water Resources Control Board Exam Conversion Sheet, chlorination, HTH solid
Show all 46 questions (43 more)

Disinfection, continued

  • A well has been out of operation for four months. What does California require before it is used again? California Code of Regulations, Title 22, section 64583
  • Chlorine is dosed at 2.5 mg/L and the residual after contact is 0.6 mg/L. What is the chlorine demand? Worked arithmetic; formula on the California State Water Resources Control Board Exam Conversion Sheet, chlorination
  • Heavily chlorinated water is flushed from a new main through a hydrant. What do hydrant dechlorination devices usually hold? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2, Basic Water Main Installation, page 2-7
  • What is disinfection meant to do? Pennsylvania DEP drinking water operator training, Module 5: Disinfection, Unit 1, page 1-2

Distribution System Design and Hydraulics 9

  • A crew shuts a hydrant quickly and a main breaks two blocks away. What most likely caused the break? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2, Valve Operation, page 2-13
  • A customer's booster pump pushes boiler water into the service line because it runs at a higher pressure than the main. What is this called? Pennsylvania DEP drinking water operator training, Module 9: Cross-Connection Control and Backflow Prevention, Unit 1, page 1-9
  • A hose is left running with its end under the surface of a tank of weed killer. What does the operator call this arrangement? Pennsylvania DEP drinking water operator training, Module 9: Cross-Connection Control and Backflow Prevention, Unit 1, page 1-2
  • A hydrant gauge reads 50 psi. How many feet of head is that? Worked arithmetic; formula on the California State Water Resources Control Board Exam Conversion Sheet, units and conversion factors
  • A main break drops system pressure below atmospheric, and water from a customer's tank is drawn back into the main. What is this called? Pennsylvania DEP drinking water operator training, Module 9: Cross-Connection Control and Backflow Prevention, Unit 1, page 1-6
  • A pump adds 12,000 gallons to a tank in 40 minutes. What is the flow rate? Worked arithmetic; formula on the California State Water Resources Control Board Exam Conversion Sheet, flow and velocity
  • A round storage tank is 30 ft in diameter and the water is 20 ft deep. How many gallons are in it? Worked arithmetic; formula on the California State Water Resources Control Board Exam Conversion Sheet, area and volume
  • What is the cross-section area of an 8-inch pipe? Worked arithmetic; formula on the California State Water Resources Control Board Exam Conversion Sheet, area and volume
  • What is the lowest operating pressure California allows in a water main at the user service line connection? California Code of Regulations, Title 22, section 64602

Equipment Operation, Maintenance and Inspections 9

  • A well's static water level is 42 ft below the ground. With the pump running, the level is 67 ft. What is the drawdown? Worked arithmetic; definition in the U.S. Geological Survey, Water Science Glossary, drawdown
  • About how many turns does it take to close a fully open 10-inch gate valve? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2, Valve Operation, page 2-13
  • On new mains 12 inches or smaller, what is the greatest distance California allows between isolation valves? California Code of Regulations, Title 22, section 64577
  • What are thrust blocks for? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2, Basic Water Main Installation, page 2-5
  • What does an altitude valve do? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2, Valves, page 2-11
  • Where should the operator stand when opening a hydrant? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2, Fire Hydrant Operation Tips, page 2-18
  • Which meter is the usual choice for a single-family service? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2, Meters, page 2-14
  • Which valve is most often used to isolate a section of main, and what should it not be used for? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2, Valves, page 2-11
  • Why does a dry-barrel hydrant have a drain that opens when the main valve is fully closed? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2, Fire Hydrants, page 2-16

Drinking Water Regulations, Management and Safety 8

  • A crew is working in a trench 6 ft deep. How close must a ladder or other way out be? California Code of Regulations, Title 8, section 1541, subsection (c)(2)
  • At what depth must a trench have a protective system against cave-ins, unless it is dug entirely in stable rock? California Code of Regulations, Title 8, section 1541.1, subsection (a)(1)
  • Before any upgrade for other factors, a distribution system is classed D1 when it serves how many people? California Code of Regulations, Title 22, section 64413.3
  • How is a lead and copper tap sample collected? California Code of Regulations, Title 22, section 64677(b)
  • How many continuing education contact hours does a Grade D1 operator need to renew the certificate? California Code of Regulations, Title 22, section 63840
  • Under California's rule, what follows one total coliform-positive routine sample, and how soon? California Code of Regulations, Title 22, section 64424(a)
  • What does California require of every employer under the Injury and Illness Prevention Program rule? California Code of Regulations, Title 8, section 3203, subsection (a)
  • Which of these calls for a Tier 1 public notice? California Code of Regulations, Title 22, section 64463.1(a)

Water Mains and Piping 9

  • A length of main has been replaced and the trench backfilled. What is the right order for putting the line back in service? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2 key points, page 2-34
  • A trench is 2.5 ft wide, 4 ft deep and 60 ft long. How many cubic yards were dug? Worked arithmetic; formula on the California State Water Resources Control Board Exam Conversion Sheet, units and conversion factors
  • How far back from the edge of an excavation must spoil and equipment be kept, unless a retaining device is used? California Code of Regulations, Title 8, section 1541, subsection (j)(2)
  • How far must a new water main be kept from a parallel pipeline that carries untreated sewage? California Code of Regulations, Title 22, section 64572(a)
  • What is the lowest flushing velocity California accepts in a main, where conditions allow the flow to be wasted? California Code of Regulations, Title 22, section 64575
  • What is the smallest nominal diameter California allows for a newly installed main in a community water system? California Code of Regulations, Title 22, section 64573
  • What should the first layer of backfill around a new main be? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2, Basic Water Main Installation, page 2-6
  • Where on a service line is the corporation stop? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2, Service Connections, page 2-8
  • Which joint is not suited to buried water main? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2, Joints, page 2-4

Water Quality and Water Sources 4

  • In groundwater terms, what is the water table? Pennsylvania DEP drinking water operator training, Module 2: Groundwater Sources of Supply and Protection, Unit 1, page 1-6
  • On the pH scale, which reading is neutral? U.S. Geological Survey, Water Science Glossary, pH
  • What does turbidity measure? Pennsylvania DEP drinking water operator training, Module 4: Water Quality and Characteristics, Unit 3, page 3-11
  • What makes a bacteriological sample siting plan acceptable? California Code of Regulations, Title 22, section 64422(a)(1)

How this list was compiled: Our own questions on the objectives the California State Water Resources Control Board lists for Grade D1 in its Expected Range of Knowledge for Drinking Water Distribution Exam (rev. 4/2020, https://www.waterboards.ca.gov/drinking_water/certlic/occupations/documents/opcert/2016/dist_range_of_know.pdf). Facts were read in Titles 8 and 22 of the California Code of Regulations (the State Water Board's September 2026 compilations and dir.ca.gov), in the Drinking Water Operator Certification Training workbooks of the Pennsylvania Department of Environmental Protection and in the U.S. Geological Survey's Water Science Glossary, all on 2026-10-11. Each question names the section or page it was written from. Licence: Own work. Every question, answer choice and explanation was written for this site from the public sources named on it. Nothing is taken from the exam, from a released or sample question, from the training workbooks' own exercises, or from another practice test.

All 40 questions

Disinfection 8

  • A 20,000 gallon section of main is dosed at 50 mg/L with 12.5 percent sodium hypochlorite that weighs 10 lb per gallon. How much hypochlorite is needed? Worked arithmetic; formula on the California State Water Resources Control Board Exam Conversion Sheet, chlorination, liquid
  • A reservoir is cleaned, disinfected and sampled, and the sample is coliform-positive. What happens next in California? California Code of Regulations, Title 22, section 64582
  • Chlorine is added to water in steps. How does the operator know the breakpoint has been passed? Pennsylvania DEP drinking water operator training, Module 25: Hypochlorite (revised 2022), Unit 4, Breakpoint Chlorination, page 4-6
Show all 40 questions (37 more)

Disinfection, continued

  • How do chloramines compare with free chlorine as a disinfectant? Pennsylvania DEP drinking water operator training, Module 5: Disinfection, Unit 1, page 1-12
  • The inside wall of a round reservoir 40 ft in diameter and 20 ft high is to be sprayed with disinfectant. What is the area of the wall? Worked arithmetic; formula on the California State Water Resources Control Board Exam Conversion Sheet, area and volume
  • What is a free chlorine residual? Pennsylvania DEP drinking water operator training, Module 5: Disinfection, Unit 2, page 2-2
  • Which method is most often used to measure chlorine residual in the field? Pennsylvania DEP drinking water operator training, Module 5: Disinfection, Unit 2, page 2-3
  • Why is the ammonia to chlorine feed ratio watched closely in chloramination? Pennsylvania DEP drinking water operator training, Module 5: Disinfection, Unit 1, page 1-12

Distribution System Design and Hydraulics 8

  • A 6-inch main carries 400 gpm. What is the velocity? Worked arithmetic; formula on the California State Water Resources Control Board Exam Conversion Sheet, flow and velocity
  • A closed 12-inch valve holds back 60 psi. What is the total force on the valve face? Worked arithmetic; formula on the California State Water Resources Control Board Exam Conversion Sheet, pounds force
  • A plating shop is rated a hazardous facility. Which protection belongs on its service? Pennsylvania DEP drinking water operator training, Module 9: Cross-Connection Control and Backflow Prevention, Unit 2, page 2-6
  • A system map is drawn at 1 inch to 200 ft. Two valves are 3.5 inches apart on the map. How far apart are they in the street? Worked arithmetic; the skill is listed in the State Water Board Expected Range of Knowledge for Drinking Water Distribution Exam, System Maps
  • The flow in a main is doubled. About how much does the head loss from friction change? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2, Friction Losses, page 2-23
  • How does a transmission main differ from a distribution main? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2, Transmission Systems, page 2-3
  • On a typical residential system, when is demand lowest? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2, Diurnal Demands, page 2-25
  • What causes cavitation at a pump? Pennsylvania DEP operator training, Module 9: Basics of Pumps and Hydraulics, Unit 4, page 4-10

Equipment Operation, Maintenance and Inspections 8

  • A magnetic flow meter has to go in a vertical pipe. Which way must the water flow? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2, Meters, page 2-15
  • A new hydrant is set on a flat stone with coarse gravel around its base. What is the gravel for? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2, Basic Fire Hydrant Installation, page 2-17
  • A tank level transmitter is ranged 0 to 40 ft over 4 to 20 mA. The signal reads 12 mA. What is the level? Worked arithmetic; formula on the California State Water Resources Control Board Exam Conversion Sheet, electrical and SCADA
  • How often should automatic air release and pressure reducing valves be inspected? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2, Valve Maintenance, page 2-28
  • What is a pressure reducing valve for? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2, Valves, page 2-12
  • When a main line valve is exercised, what should be recorded? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2, Valve Maintenance, page 2-28
  • Where are vacuum relief valves commonly placed, and why? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2, Valves, page 2-12
  • Which meters measure low flows inaccurately? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2, Meters, page 2-14

Drinking Water Regulations, Management and Safety 4

  • A distribution system is classed D2. What grades must its chief operator and its shift operator hold at least? California Code of Regulations, Title 22, sections 63770 and 64413.7
  • Besides a high school diploma or GED, what does California ask of an applicant for the D2 exam? California Code of Regulations, Title 22, section 63780(c)
  • For how long must records of main flushing and of reservoir inspection and cleaning be kept? California Code of Regulations, Title 22, section 64604(c)
  • What is the maximum residual disinfectant level for chlorine in California drinking water? California Code of Regulations, Title 22, section 64533.5

Water Mains and Piping 8

  • A main has good walls but poor flow. What does cleaning and lining do for it? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2, Pipeline Rehabilitation, page 2-33
  • An 8-inch main is to be flushed at 2.5 ft/sec. About what flow does that take? Worked arithmetic; formula on the California State Water Resources Control Board Exam Conversion Sheet, flow and velocity
  • At what positions on the main is a corporation stop typically tapped? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2, Service Connections, page 2-8
  • How far must a new water main be kept from a parallel storm drain? California Code of Regulations, Title 22, section 64572(b)
  • Night flow into a metered district creeps up over several days. What does that suggest? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2, Leak Detection, page 2-31
  • Two pipes of the same size are compared. One has a C-factor of 140 and the other 80. What does that say? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2, Friction Losses, page 2-22
  • What does tuberculation do to an old iron main? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2, Friction Losses, page 2-23
  • Which facts decide the size and type of a thrust block? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 2, Basic Water Main Installation, page 2-6

Water Quality and Water Sources 4

  • Two different metals are joined in a service line, and one of them corrodes at the joint. What kind of corrosion is this? Pennsylvania DEP drinking water operator training, Module 20: Corrosion Control and Sequestering (April 2017), Unit 1, page 1-2
  • Water sits in a storage tank far longer than it should. What is the usual effect on quality? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 3 key points, page 3-11
  • What is a cone of depression? Pennsylvania DEP drinking water operator training, Module 2: Groundwater Sources of Supply and Protection, Unit 3, page 3-4
  • Which three things can be monitored to judge whether booster chlorination is working in the distribution system? Pennsylvania DEP drinking water operator training, Module 8: Distribution Systems (revised January 2023), Unit 4, page 4-16

How this list was compiled: Our own questions on the objectives the California State Water Resources Control Board lists for Grade D2 in its Expected Range of Knowledge for Drinking Water Distribution Exam (rev. 4/2020, https://www.waterboards.ca.gov/drinking_water/certlic/occupations/documents/opcert/2016/dist_range_of_know.pdf), with the weight on the objectives that begin at D2. Facts were read in Title 22 of the California Code of Regulations (the State Water Board's September 2026 compilations), in the operator certification training workbooks of the Pennsylvania Department of Environmental Protection and in the U.S. Geological Survey's Water Science Glossary, all on 2026-10-11. Each question names the section or page it was written from. Licence: Own work. Every question, answer choice and explanation was written for this site from the public sources named on it. Nothing is taken from the exam, from a released or sample question, from the training workbooks' own exercises, or from another practice test.

How it works

This D1 water distribution practice test for California follows the state's Expected Range of Knowledge, with a second set for D2. It is unofficial and not affiliated with, endorsed by or sponsored by the California State Water Resources Control Board.

Read the full guide

D1 or D2

Each question belongs to one grade. The D1 set stays on the objectives the outline lists from D1 up. The D2 set adds those that begin at D2: chloramines, head loss, map scales, thrust block sizing. A D1 water certification practice test means the same exam.

Where the answers come from

Rule questions cite Title 22 or Title 8 of the California Code of Regulations by section. Operating questions cite Pennsylvania's public operator training modules by page. Math uses the factors on the state's Exam Conversion Sheet.

  • Know California's own numbers: 20 psi minimum pressure, 2.5 feet per second flushing velocity, a 4-inch minimum main, valves no more than 1,320 feet apart.
  • One psi is 2.31 feet of water. Most pressure, tank and well questions turn on that one factor.

Questions and answers

Is there a D2 water certification practice test here?

Yes. The California water distribution D2 practice test is the second set: 40 questions of its own in the D2 proportions, none repeated from D1. The D2 exam also covers every D1 objective, so work both sets.

How many questions are on the D1 and D2 exams?

The state's outline counts 100 questions at each grade. The exams are given on a computer at test centers all year, with a built-in calculator and the state's formula sheet. The pages cited here give no time limit or pass mark.

Who can take the D1 exam?

An applicant needs a high school diploma or GED. The Basic Small Water System Operations course, or a year operating a piping system with pumps, valves and storage tanks, can stand in for it. D2 adds one specialized training course in water supply principles.

Can I use this as a California water distribution Grade 1 study guide?

As the practice half of one. Each explanation names the Title 22 section or the free public module page to read next. The state's own list for a water distribution study guide in California is the outline, the regulations and EPA's quick reference guides.

Which systems need a D1 or D2 operator?

A system serving 1,000 people or fewer is class D1 and one serving 1,001 through 10,000 is D2, before any upgrade for other factors. A D2 system needs a D2 chief operator and at least a D1 shift operator.

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