- How the Professional Hydrologist Exam Is Actually Structured
- Part I Fundamentals: Domains 1-4
- Part II Surface Water: Domains 5-7
- Part II Groundwater: Domains 8-10
- Water Quality: Why It Has No Domain Line Here
- Reading the Weights Side by Side
- Format, Fees and Eligibility Mechanics
- Sequencing Your Preparation by Domain
- Frequently Asked Questions
- The "10 domains" are headings across components and alternatives; no single exam tests all ten.
- The ordinary path is Part I Fundamentals plus one Part II specialty, Surface Water or Groundwater.
- Surface Water is weighted 31/46/23; Groundwater is 51/38/11. Each specialty totals 100% on its own.
- Each exam requires 70% to pass, and three failures bar further AIH applications.
How the Professional Hydrologist Exam Is Actually Structured
The title of this guide promises ten content areas, and that count deserves an immediate clarification: it is a count of supported headings across the American Institute of Hydrology (AIH) examination components, not ten domains in one test. The Professional Hydrologist (PH) credential, awarded by AIH, is built from two separate exams on the ordinary documented path: a common Part I Fundamentals exam and one applicable Part II specialty exam. Candidates who hold a valid Hydrologic Technician (HIT) credential do not repeat Part I.
That means a Surface Water candidate meets Domains 1-4 and 5-7. A Groundwater candidate meets Domains 1-4 and 8-10. Nobody sits for all ten. Domains 5-7 and 8-10 share the same three heading names but carry entirely different weights, because the two specialties are scored and blueprinted independently.
Published specifications describe each part as approximately 100 questions over about four hours, for roughly 200 questions and eight hours across the two separate exams. These are two exams, not one marathon sitting. Part I is explicitly multiple choice, and practice and development materials use multiple choice as well. The split between scored and unscored questions has not been disclosed.
Part I Fundamentals: Domains 1-4
The Fundamentals exam is common to every PH candidate regardless of specialty. Its four headings carry published allocations of approximately 20, 45, 30 and 5 questions. These are approximate question counts rather than printed percentages, so treat them as guidance on emphasis, not as exact quotas.
Domain 1: Water Quantity and Quality in the Field
Water Quantity and Quality in the Field (about 20 questions)
This is the field-practice domain: how hydrologic data is actually obtained and how measurements behave outside a textbook.
- Field measurement of streamflow and stage, and the practical sources of error in each approach
- Field collection and handling of water samples for quality assessment
- Instrument selection, calibration and maintenance concepts
- Recognizing when a field reading is implausible and needs rechecking
Domain 2: Quantity and Timing of Flow
Quantity and Timing of Flow (about 45 questions)
At roughly 45 questions, this is the heaviest Fundamentals heading by allocation. It is where quantitative hydrology concentrates, so candidates who underinvest here are exposed.
- Rainfall-runoff relationships and the factors that control how much water moves and how fast
- Hydrograph concepts: peak, timing, recession and volume
- Flow frequency and the meaning of recurrence for planning and design
- Water-balance reasoning that links precipitation, evaporation, storage and flow
Domain 3: Assessing Water Quality Conditions, Impacts and Sources
Assessing Water Quality Conditions, Impacts and Sources (about 30 questions)
Even candidates headed to quantity-focused specialties face meaningful water-quality content here, because Fundamentals is common to all paths.
- Interpreting water-quality data to characterize conditions in a water body
- Distinguishing point and nonpoint contributions and tracing likely sources
- Linking pollutant loads and concentrations to flow conditions
- Evaluating impacts on receiving waters
Domain 4: Statistical Analyses
Statistical Analyses (about 5 questions)
The smallest allocation, but statistics underpin frequency analysis and data interpretation across the rest of the exam, so it pays off beyond its own question count.
- Descriptive statistics and distributions applied to hydrologic records
- Appropriate use of central tendency, variability and trend concepts
- Recognizing limitations in short or biased data records
For how the exam feels once you are inside it, see How Hard Is the PH Exam?.
Part II Surface Water: Domains 5-7
The Surface Water specialty is blueprinted at 31%, 46% and 23% across its three headings, totaling 100% on its own. The detail pages describe the part as 100 questions, while the introductions call it approximate, so plan around "about 100."
Domain 5: Collection and Inventory of Basic Hydrological Data (31%)
The data-acquisition foundation for surface-water work.
- Stream gaging methods and the construction of stage-discharge relationships
- Precipitation, evaporation and other climatic data networks
- Evaluating data quality, gaps and record continuity
- Organizing and inventorying hydrologic records for later analysis
Domain 6: Interpretation, Analysis & Modeling of Hydrological Processes (46%)
The single largest category in the Surface Water exam, and the one that should receive the most study time on this path.
- Hydrologic and hydraulic analysis of watersheds and channels
- Flood frequency estimation and interpretation of results
- Rainfall-runoff modeling: selecting an approach, setting parameters, judging output
- Understanding model assumptions, calibration and uncertainty
Domain 7: Design Hydrological Systems (23%)
Applying analysis to the sizing and performance of water-related infrastructure and management systems.
- Design-flow selection and the role of acceptable risk
- Conveyance, storage and control-structure concepts
- Stormwater and flood-management system reasoning
- Checking whether a proposed design meets its hydrologic objective
Part II Groundwater: Domains 8-10
The Groundwater specialty reuses the three heading names but shifts the emphasis sharply, at 51%, 38% and 11%, again totaling 100% separately.
Domain 8: Collection and Inventory of Basic Hydrological Data (51%)
The largest Groundwater category: more than half the specialty exam concerns how subsurface data is gathered and inventoried.
- Well construction, monitoring-well networks and water-level measurement
- Aquifer testing and the field data it generates
- Subsurface characterization and records of geologic and hydraulic properties
- Groundwater sampling approaches and data-quality concerns
Domain 9: Interpretation, Analysis & Modeling of Hydrological Processes (38%)
Turning groundwater data into understanding.
- Interpreting water-level maps, flow directions and gradients
- Analyzing aquifer-test results to estimate hydraulic properties
- Groundwater flow modeling concepts, assumptions and limitations
- Surface water and groundwater interaction
Domain 10: Design Hydrological Systems (11%)
The smallest specialty heading, but still examinable.
- Well and wellfield design concepts
- Dewatering, recharge and groundwater-management systems
- Evaluating whether a design achieves its yield or protection objective
Water Quality: Why It Has No Domain Line Here
AIH's current requirements and bylaws do recognize Water Quality as a specialty. However, a current standalone Water Quality exam outline, with verified objectives and weights, could not be confirmed. For that reason this guide does not assign it a domain line, a timer or a weighting.
Note also that Domain 3 in Fundamentals does cover water-quality assessment for every candidate, so quality content is not absent from the exam path; it simply is not a separately verified specialty outline.
Reading the Weights Side by Side
The three heading names repeat across specialties, which invites confusion. This table keeps the alternatives apart. Do not add percentages across the two specialty columns; a candidate takes one or the other.
| Heading | Surface Water (Domains 5-7) | Groundwater (Domains 8-10) |
|---|---|---|
| Collection and Inventory of Basic Hydrological Data | 31% | 51% |
| Interpretation, Analysis & Modeling of Hydrological Processes | 46% | 38% |
| Design Hydrological Systems | 23% | 11% |
| Specialty total | 100% | 100% |
The practical reading: a Surface Water candidate is rewarded for analytical and modeling strength, while a Groundwater candidate is rewarded for command of field data collection and inventory. Same words, different centers of gravity. Choosing your specialty is partly choosing which skill the exam will weight most. For related decisions on timing and effort, the PH Study Guide and PH Cheat Sheet pair well with this breakdown.
Format, Fees and Eligibility Mechanics
What the exam allows and requires
- Passing minimum: 70% on each exam. Three failures bar further AIH applications, per the examination page. See PH Passing Score for more.
- Language and tools: English; open book, references and notes are described, along with calculators.
- Delivery: AIH administers virtual proctoring; no commercial testing vendor is verified, and Certemy serves as the application platform.
- Unresolved details: The prohibition on reference computers sits awkwardly beside virtual delivery, so do not assume digital references are permitted without confirming. The four-hour Fundamentals specification also conflicts with a December 11, 2026 event listing of 9 a.m. to noon.
- Not disclosed: the overall PH pass rate and the scored/unscored split. Our PH pass rate article covers what can and cannot be said.
Standard fees
The standard fee schedule is a $100 application, $200 for Part I and $200 for Part II, for a calculated initial total of $500 before dues. Annual PH dues are $175 (prorated in the first year), and recertification is $65 every five years. Currency is not explicitly labeled, and no general member versus non-member exam fee pair is published. A September-December 2026 early-career Fundamentals offer waives upfront application and exam fees, with $150 payable only after passing and accepting HIT; it is not a free PH or a Part II discount. Full numbers are in PH Certification Cost.
Eligibility in brief
Under the January 30, 2026 bylaws (Sections 3.2 and 3.4), candidates need relevant education plus qualifying post-degree experience: five years with a bachelor's, four with a master's, three with a doctorate, along with three referees. Coursework expectations include five semester or eight quarter hours each in chemistry, physics and calculus, plus basic hydrology and specialty hours with a Category I minimum. The Approved Coursework List supplies eligibility examples, not exam domains. Details live in PH Requirements, and scheduling in PH Exam Dates.
Key Takeaway
Eligibility and examination content are separate systems. Passing the coursework check does not map to a domain, and the domains do not tell you which courses count. Treat them as two checklists.
Sequencing Your Preparation by Domain
One short note on method, tied to the weights above: schedule by allocation, not by comfort. Fundamentals first, because Part I is required for nearly everyone and Domain 2's roughly 45 questions are the biggest single block there. Then your specialty, with study time proportional to its largest category.
Fundamentals: flow first
- Spend the most time on Domain 2, Quantity and Timing of Flow
- Layer in Domain 3 water-quality interpretation
- Touch Domain 1 field practice and Domain 4 statistics lightly but regularly
Specialty heavyweight
- Surface Water: weight Domain 6 modeling and analysis (46%)
- Groundwater: weight Domain 8 data collection and inventory (51%)
Design and integration
- Cover the design heading for your specialty (23% or 11%)
- Work mixed multiple-choice sets and assemble your reference materials
Since the exam is described as open reference, organize your notes by domain so retrieval is fast under time pressure. If you are weighing the effort against the career payoff, see Is the PH Certification Worth It?, PH Salary Guide and PH Jobs. When you are ready to test yourself against domain-style questions, use the PH practice test and track results by domain on the main practice site.
Readers confirming the basics can start with What Is PH? and PH Training, and the same domain breakdown is summarized at PH Exam Domains 2026.
Frequently Asked Questions
No. The ten are headings across components and alternatives. The ordinary path is Part I Fundamentals (Domains 1-4) plus one Part II specialty: Surface Water (Domains 5-7) or Groundwater (Domains 8-10).
It depends on the exam. In Fundamentals, Quantity and Timing of Flow has the largest allocation at about 45 questions. In Surface Water, Interpretation, Analysis & Modeling is largest at 46%. In Groundwater, Collection and Inventory is largest at 51%.
No. The 20/45/30/5 figures are approximate question counts, not printed percentages. The Surface Water and Groundwater figures are published percentages that total 100% within each specialty.
AIH's requirements and bylaws recognize Water Quality, but a current standalone exam outline was not verified. Historical development categories exist, but they are not confirmed current objectives, so check with AIH directly.
The passing minimum is 70% on each exam. According to the examination page, three failures bar further AIH applications, so treat each attempt as consequential and prepare accordingly.