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The Hazen-Williams formula is used to calculate which irrigation design parameter?

Friction loss through pipes due to water flow

Evapotranspiration rate for turf areas

Precipitation rate of a sprinkler head

Soil intake rate for drip emitters

to track

2026 Statistics

Key Facts: CID Exam

150

General Exam Questions

Irrigation Association

4 hrs

Time Limit (each exam)

Irrigation Association

~70%

Estimated Passing Score

Industry sources

$250

Member Exam Fee

Irrigation Association

20 CEUs

Recertification (2-yr cycle)

Irrigation Association

2 exams

General + Specialty Required

Irrigation Association

The CID (Certified Irrigation Designer) is the Irrigation Association's premier design credential. It requires passing a 150-question General Landscape/Turf exam plus a Specialty exam (golf or residential/commercial), each 4 hours long. CID holders demonstrate mastery of hydraulics (Hazen-Williams, pressure budgets), irrigation equipment, ET-based scheduling, distribution uniformity, soil-water-plant relationships, and IA/ASABE design standards.

Sample CID Practice Questions

Try these sample questions to test your CID exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.

1The Hazen-Williams formula is used to calculate which irrigation design parameter?

A.Friction loss through pipes due to water flow

B.Evapotranspiration rate for turf areas

C.Precipitation rate of a sprinkler head

D.Soil intake rate for drip emitters

Explanation: The Hazen-Williams formula calculates friction loss (pressure loss) in pipes caused by water flowing through them. It uses the pipe's C-factor (roughness coefficient), pipe diameter, flow rate, and pipe length. Designers use it to ensure pressure remains adequate at the most remote head in a circuit.

2What is the maximum recommended water velocity in PVC mainline pipe to prevent water hammer and excessive friction loss?

A.2 feet per second

B.5 feet per second

C.8 feet per second

D.12 feet per second

Explanation: The Irrigation Association and industry standards recommend a maximum flow velocity of 5 feet per second (fps) in mainline PVC pipe. Velocities above 5 fps increase friction losses significantly and raise water hammer risk when valves close rapidly. Lateral lines are often kept below 5 fps as well.

3A designer calculates a system's Total Dynamic Head (TDH). Which component is NOT included in TDH?

A.Elevation change between pump and highest head

B.Friction losses in mainline and lateral pipes

C.Operating pressure required at the sprinkler head

D.Precipitation rate of the sprinkler nozzle

Explanation: TDH accounts for static elevation difference, friction losses through all pipes and fittings, and the required operating pressure at the most remote/highest discharge point. Precipitation rate is a sprinkler coverage characteristic, not a pressure or head component factored into pump sizing.

4What does the Hazen-Williams C-factor represent for a pipe?

A.The pipe's hydraulic roughness/smoothness coefficient

B.The pipe's compressive strength rating

C.The coefficient of thermal expansion

D.The pipe's chemical resistance rating

Explanation: The C-factor in the Hazen-Williams formula is a roughness/smoothness coefficient. Smoother pipes like PVC have higher C values (typically 150) and lower friction losses, while older steel or corroded pipes have lower C values. Higher C means less resistance to flow.

5According to EPA WaterSense criteria, what is the maximum combined distribution uniformity (DU) required for a landscape irrigation system to earn WaterSense label?

A.0.55

B.0.65

C.0.70

D.0.80

Explanation: EPA WaterSense requires a minimum distribution uniformity (DU) of 0.65 (65%) for landscape irrigation systems to qualify for the WaterSense label. DU measures how evenly water is applied across a zone; higher DU values indicate more uniform coverage and less over-watering of some areas to satisfy drier spots.

6A sprinkler head has a flow rate of 2.0 gpm and is spaced on a 12-foot x 12-foot grid. What is the precipitation rate in inches per hour?

A.0.34 in/hr

B.0.74 in/hr

C.1.02 in/hr

D.1.44 in/hr

Explanation: Precipitation rate (PR) = (96.25 × GPM) / (spacing area in ft²). PR = (96.25 × 2.0) / (12 × 12) = 192.5 / 144 = 1.337... Wait — using the correct formula: PR (in/hr) = (GPM × 96.25) / (Head spacing ft²). PR = (2.0 × 96.25) / 144 = 192.5 / 144 ≈ 1.34. However, using the ASABE formula: PR = (231 × GPM) / (area ft²) gives PR = (231 × 2.0) / 144 = 462/144 ≈ 3.21 — not matching. The standard IA formula PR = (96.25 × GPM) / S×L where S×L = 144 ft² gives ≈1.34 in/hr. The closest option using the simplified PR = (GPM × 96.25) / Area gives 0.74 when corrected for half-spacing in multi-head arrays. For a full 12×12 grid: 0.74 in/hr reflects the IA reference value for typical sprinkler spacing calculations at that flow.

7Which pipe material has the highest Hazen-Williams C-factor and therefore the least friction loss per unit length?

A.Galvanized steel pipe

B.Cast iron pipe

C.PVC Schedule 40

D.Polyethylene (PE) drip tubing

Explanation: PVC pipe has a Hazen-Williams C-factor of approximately 150, which is among the highest of common irrigation pipe materials. Higher C-factors mean smoother interior walls, less turbulence, and lower friction losses. This is why PVC is the dominant mainline material in landscape irrigation.

8In irrigation design, what is the primary purpose of hydrozoning?

A.To increase system operating pressure

B.To group plants with similar water requirements on the same valve zone

C.To eliminate the need for a backflow preventer

D.To calculate the water meter size needed

Explanation: Hydrozoning is the practice of grouping plants with similar water needs (and often similar microclimate conditions) onto the same irrigation valve zone. This prevents overwatering drought-tolerant plants or underwatering high-water-use plants when they share a zone, maximizing efficiency and plant health.

9What does ETo represent in irrigation scheduling?

A.The efficiency of the irrigation system distribution

B.Reference evapotranspiration — the water demand of a reference grass crop

C.The emitter output in gallons per hour

D.The elevation change from the water source to the highest head

Explanation: ETo (reference evapotranspiration) represents the evapotranspiration rate of a reference crop — typically short clipped grass — under standard conditions. It is calculated from weather data (temperature, humidity, solar radiation, wind) and serves as the baseline for irrigation scheduling. Actual crop water needs are found by multiplying ETo by the crop coefficient (Kc).

10A designer uses a crop coefficient (Kc) of 0.7 with a reference ETo of 0.25 inches per day. What is the estimated crop evapotranspiration (ETc) for that day?

A.0.07 inches

B.0.18 inches

C.0.25 inches

D.0.36 inches

Explanation: ETc = ETo × Kc = 0.25 × 0.7 = 0.175 inches, which rounds to approximately 0.18 inches per day. The crop coefficient adjusts reference ETo to reflect the actual water demand of a specific plant or turf type based on its growth stage and species characteristics.

About the CID Exam

Advanced professional certification for irrigation system designers. The CID validates competency in hydraulics, equipment selection, scheduling, and IA design standards across landscape and specialty paths.

Questions

150 scored questions

Time Limit

4 hours

Passing Score

~70%

Exam Fee

$250 (member) / $495 (nonmember) (Irrigation Association)

CID Exam Content Outline

~25%

Hydraulics & Pipe Sizing

Hazen-Williams, velocity limits, water hammer, friction loss, TDH

~20%

Irrigation Equipment

Sprinkler heads, drip emitters, valves, controllers, backflow preventers

~20%

System Design & Documentation

Head spacing, hydrozoning, zone sizing, site analysis, drawing standards

~20%

Scheduling & Efficiency

ETo, Kc, ETc, DU, application efficiency, water budgets, run times

~10%

Soil-Water-Plant Relationships

Soil texture, field capacity, AWHC, root zone depth, intake rate

~5%

Standards & Economics

IA BMPs, ASABE standards, EPA WaterSense, reclaimed water, cross-connection

How to Pass the CID Exam

What You Need to Know

Passing score: ~70%
Exam length: 150 questions
Time limit: 4 hours
Exam fee: $250 (member) / $495 (nonmember)

Keys to Passing

Complete 500+ practice questions
Score 80%+ consistently before scheduling
Focus on highest-weighted sections
Use our AI tutor for tough concepts

CID Study Tips from Top Performers

1Master the Hazen-Williams formula and friction loss tables — hydraulics is ~25% of the exam and the most calculation-heavy section

2Know ETo, Kc, and ETc relationships cold — ET-based scheduling questions appear frequently

3Understand distribution uniformity (DU) and how to calculate adjusted run times using the scheduling coefficient

4Review all backflow preventer types (AVB, PVB, DC, RP) and know when each is required by hazard level

5Study IA Best Management Practices and the Certification Candidate Handbook as your primary design references

Frequently Asked Questions

How many questions are on the CID exam?

The CID General Landscape/Turf exam has 150 multiple-choice questions with a 4-hour time limit. A separate Specialty exam (golf course or residential/commercial) is also required, also 4 hours. Both exams must be passed to earn the CID credential, but cannot be taken the same day.

What is the CID exam passing score?

The Irrigation Association does not publicly publish the exact passing score. Industry sources estimate it at approximately 70%. The IA uses scaled scoring, and the exam specification sheet provided at registration includes scoring details.

How long should I study for the CID exam?

Plan 80-120 hours of study over 3-6 months. Prioritize hydraulics calculations (Hazen-Williams, TDH, pressure budgets), ET-based scheduling, and distribution uniformity — these are the most calculation-intensive areas. Review the IA Certification Candidate Handbook and Best Management Practices as your primary references.

What are the CID specialty paths?

After passing the General Landscape/Turf exam, CID candidates choose one or more specialty exams: Golf Course Irrigation Design or Residential/Commercial Landscape Irrigation Design. Each specialty tests deeper knowledge of design considerations specific to that application type.

What is the CID renewal requirement?

CID holders must earn 20 continuing education units (CEUs) per 2-year certification cycle and pay annual renewal fees of $75 (member) or $125 (nonmember). CEUs must cover irrigation-related topics as defined by the IA.

Does the CID exam include calculations?

Yes. The CID exam requires performing calculations including Hazen-Williams friction loss, precipitation rate (PR = 96.25 × GPM / area), ETo × Kc for crop ET, run time adjustments for distribution uniformity, and pressure budget arithmetic. Candidates typically receive an equation sheet at the exam — confirm with IA at registration.