California Water Operator Exam Pass Rates (SWRCB Data)
Pass rates for the California T1 to T5, D1 to D5 and wastewater Grade 1 to 5 exams from State Water Board statistics, 2023 to 2025, plus certificate counts and the age of wastewater operators.
About six in ten candidates pass a California drinking water operator exam. In wastewater it is fewer than half.
The State Water Resources Control Board publishes the results of every exam period, split by grade. We added up the half-year tables into calendar years, so you can compare the grades directly.
This site is an independent exam trainer. Certificates are issued by the State Water Board, not by us, and we are not affiliated with the Board or its testing provider.
In short
- 59.3 percent of 2,353 treatment exam candidates passed in 2025, down from 63.4 percent in 2023.1
- Distribution exams passed 62.4 percent of 3,933 candidates in 2025.2
- The T5 exam is the hardest drinking water exam: 36.1 percent passed in 2025.1
- Wastewater exams passed only 43.4 percent of all computer-based attempts from 2021 to 2024, and Grade 5 just 24.1 percent.3
- More than a third of certified wastewater operators were over 55 in March 2025.3
Treatment exams T1 to T5
The figures add the two half-year periods the Board reports for each year.1
159.3 percent in 2025
1,395 of 2,353 treatment candidates passed in 2025. The rate was 63.4 percent in 2023 and 61.6 percent in 2024.1
2T1: 58.0 percent
332 of 572 candidates passed the entry level T1 exam in 2025, the lowest T1 rate of the three years.1
3T2: 60.9 percent
772 of 1,267 passed in 2025. T2 is by far the most taken treatment exam.1
4T5: 36.1 percent
Only 26 of 72 candidates passed the top grade in 2025. T5 has been the hardest treatment exam in every year since 2023.1
| Grade | 2023 | 2024 | 2025 | Candidates 2025 |
|---|---|---|---|---|
| T1 | 64.1% | 62.5% | 58.0% | 572 |
| T2 | 63.9% | 61.0% | 60.9% | 1,267 |
| T3 | 66.8% | 64.8% | 63.7% | 303 |
| T4 | 62.1% | 63.2% | 51.8% | 139 |
| T5 | 38.9% | 49.4% | 36.1% | 72 |
| All grades | 63.4% | 61.6% | 59.3% | 2,353 |
Distribution exams D1 to D5
562.4 percent in 2025
2,454 of 3,933 distribution candidates passed in 2025, close to 63.4 percent in 2023 and 62.8 percent in 2024. More people take distribution exams than treatment exams.2
6D2: 64.4 percent
1,150 of 1,787 candidates passed in 2025. D2 had the highest pass rate of all distribution grades in each of the three years.2
7D5: 56.6 percent
81 of 143 passed in 2025. Unlike treatment, the top distribution grade is not far behind the others.2
| Grade | 2023 | 2024 | 2025 | Candidates 2025 |
|---|---|---|---|---|
| D1 | 61.9% | 61.8% | 62.8% | 1,027 |
| D2 | 65.7% | 65.1% | 64.4% | 1,787 |
| D3 | 63.3% | 62.6% | 59.9% | 681 |
| D4 | 56.6% | 59.1% | 57.6% | 295 |
| D5 | 62.2% | 51.7% | 56.6% | 143 |
| All grades | 63.4% | 62.8% | 62.4% | 3,933 |
Wastewater exams Grade 1 to 5
The wastewater program reports computer-based exam results in its Advisory Committee statistics, which use a different format from the drinking water tables.3
843.4 percent since 2021
From the start of computer-based testing on February 20, 2021 to the end of 2024, 2,281 of 5,255 wastewater exam attempts passed.3
9Grade 1 and 2: 54 percent
Grade 1 passed 766 of 1,416 attempts and Grade 2 passed 793 of 1,460 over the same period.3
10Grade 3 to 5: 24 to 34 percent
Grade 3 passed 34 percent (461 of 1,342), Grade 4 26 percent (101 of 388) and Grade 5 24 percent (160 of 649). From Grade 3 on, most candidates fail.3
11Second half of 2024: 43.0 percent
318 of 739 candidates passed between July and December 2024, with Grade 5 at 22 percent.3
| Grade | July to Dec 2023 | July to Dec 2024 | 2021 to 2024 |
|---|---|---|---|
| Grade 1 | 57% | 51% | 54% |
| Grade 2 | 59% | 52% | 54% |
| Grade 3 | 37% | 38% | 34% |
| Grade 4 | 26% | 28% | 26% |
| Grade 5 | 23% | 22% | 24% |
Certificates and age
126,235 valid wastewater certificates
At the end of December 2024 there were 6,235 valid wastewater certificates, including 691 operators in training. Grade 3 was the largest group with 1,806 certificates.3
13Average age 47.5
The average certified wastewater operator was 47.5 years old in March 2025. 34.3 percent were over 55, and at Grade 4 and 5 about half were.3
With half of the Grade 4 and 5 operators over 55, many of the most senior certificate holders will reach retirement age within the next ten years.
You can find out where you stand with a free practice test.
Common questions
What is the pass rate of the California T2 exam?
60.9 percent of 1,267 candidates passed in 2025.1
Which California water operator exam is the hardest?
By pass rate, wastewater Grade 5 (24 percent from 2021 to 2024) and treatment T5 (36.1 percent in 2025).31
Are treatment exams harder than distribution exams?
Slightly: 59.3 against 62.4 percent in 2025.12
Writing about this topic yourself? You are welcome to use all the numbers, with a link to this page. Pick a format and copy it with one click.
<a href="https://californiawatercertification.com/blog/california-water-operator-exam-pass-rates/">California Water Operator Exam Pass Rates (SWRCB Data)</a>, CaliforniaWaterCertification.comMarsh, E. (2026). California Water Operator Exam Pass Rates (SWRCB Data). CaliforniaWaterCertification.com. https://californiawatercertification.com/blog/california-water-operator-exam-pass-rates/
Marsh, Evan. "California Water Operator Exam Pass Rates (SWRCB Data)." CaliforniaWaterCertification.com, 2026, californiawatercertification.com/blog/california-water-operator-exam-pass-rates/
Sources
Yearly rates are our sums of the Board's half-year tables. The Board updates its results pages after each exam period, so check them for newer figures.
- State Water Resources Control Board: Water Treatment Exam Results (waterboards.ca.gov)
- State Water Resources Control Board: Water Distribution Exam Results (waterboards.ca.gov)
- State Water Resources Control Board: Wastewater Operator Certification Program statistics, Advisory Committee meeting April 9, 2025 (waterboards.ca.gov)
Enough reading, time to practice
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