2026/2027 Texas Class D Water License Exam Questions and
Answers | Verified Answers with Detailed Rationales (2026/2027
Edition)
SECTION 1: RULES, REGULATIONS, AND GENERAL KNOWLEDGE
1. Under 30 TAC Chapter 290, Subchapter D, what is the minimum number of
bacteriological samples required per month for a community public water system
serving a population between 3,301 and 4,100?
A. 1 sample per month
B. 3 samples per month
C. 4 samples per month
D. 5 samples per month
Correct Answer: C. 4 samples per month
Rationale: Per 30 TAC §290.109(b), the minimum monthly bacteriological sampling
requirement for community water systems serving 3,301–4,100 persons is 4 samples.
Option A applies to systems serving 1,000 or fewer. Option B applies to 2,501–3,300.
Option D applies to 4,101–5,000. The sample frequency escalates with population to
ensure adequate statistical representation of water quality.
2. A Class D water operator in Texas is primarily responsible for operating systems that
use which of the following treatment complexities?
,A. Conventional surface water treatment including coagulation, flocculation,
sedimentation, and filtration
B. Disinfection only, or groundwater systems not under the direct influence of surface
water with no treatment other than disinfection
C. Lime-soda softening and reverse osmosis membrane systems
D. Advanced oxidation processes and granular activated carbon adsorption
Correct Answer: B. Disinfection only, or groundwater systems not under the direct
influence of surface water with no treatment other than disinfection
Rationale: TCEQ Class D licensure scope covers entry-level operations, specifically
systems where treatment is limited to disinfection or groundwater systems not under
direct influence of surface water (GWUDI) without additional treatment. Option A
describes Class C and higher surface water treatment. Options C and D describe
advanced treatment requiring Class B or A certification. Class D operators must
recognize their operational boundaries under 30 TAC Chapter 30, Subchapter K.
3. Which of the following waterborne diseases is MOST commonly associated with
inadequate disinfection of drinking water and is caused by the protozoan Giardia
lamblia?
A. Hepatitis A
B. Giardiasis
C. Legionellosis
D. Cryptosporidiosis
,Correct Answer: B. Giardiasis
Rationale: Giardia lamblia (also Giardia intestinalis) causes giardiasis, a gastrointestinal
illness frequently linked to inadequate surface water treatment or disinfection failure.
Option A is viral. Option C is caused by Legionella pneumophila, typically associated with
building plumbing systems and warm water aerosols, not primarily inadequate primary
disinfection. Option D is caused by Cryptosporidium, which is highly chlorine-resistant
and requires filtration or UV for effective removal, making it less directly associated with
simple disinfection inadequacy than Giardia.
4. Under the federal Safe Drinking Water Act and TCEQ rules, a public water system
must provide a Consumer Confidence Report (CCR) to its customers no later than which
date annually?
A. January 1
B. April 1
C. July 1
D. October 1
Correct Answer: C. July 1
Rationale: The CCR must be delivered to customers by July 1 of each year, covering data
from the previous calendar year. This deadline is mandated by 40 CFR §141.155 and
adopted by reference in TCEQ rules. Option A is incorrect. Option B is the deadline for
systems on quarterly monitoring to submit compliance samples. Option D is beyond the
regulatory deadline and would constitute a violation.
, 5. A public water system in Texas is classified as a "community water system" if it
serves at least how many persons year-round?
A. 10 persons
B. 15 service connections
C. 25 persons
D. 50 persons
Correct Answer: C. 25 persons
Rationale: Per 30 TAC §290.38(32), a community water system serves at least 25
persons year-round or has at least 15 service connections. However, the question asks
for the person threshold, which is 25. Option A is below the threshold. Option B
describes the service connection threshold, not persons. Option D exceeds the
minimum requirement. Both 15 connections OR 25 persons define the classification.
6. Which physical characteristic of water is MOST directly responsible for causing
corrosion in distribution system pipes when elevated?
A. Turbidity
B. pH
C. Temperature
D. Color
Correct Answer: B. pH
Answers | Verified Answers with Detailed Rationales (2026/2027
Edition)
SECTION 1: RULES, REGULATIONS, AND GENERAL KNOWLEDGE
1. Under 30 TAC Chapter 290, Subchapter D, what is the minimum number of
bacteriological samples required per month for a community public water system
serving a population between 3,301 and 4,100?
A. 1 sample per month
B. 3 samples per month
C. 4 samples per month
D. 5 samples per month
Correct Answer: C. 4 samples per month
Rationale: Per 30 TAC §290.109(b), the minimum monthly bacteriological sampling
requirement for community water systems serving 3,301–4,100 persons is 4 samples.
Option A applies to systems serving 1,000 or fewer. Option B applies to 2,501–3,300.
Option D applies to 4,101–5,000. The sample frequency escalates with population to
ensure adequate statistical representation of water quality.
2. A Class D water operator in Texas is primarily responsible for operating systems that
use which of the following treatment complexities?
,A. Conventional surface water treatment including coagulation, flocculation,
sedimentation, and filtration
B. Disinfection only, or groundwater systems not under the direct influence of surface
water with no treatment other than disinfection
C. Lime-soda softening and reverse osmosis membrane systems
D. Advanced oxidation processes and granular activated carbon adsorption
Correct Answer: B. Disinfection only, or groundwater systems not under the direct
influence of surface water with no treatment other than disinfection
Rationale: TCEQ Class D licensure scope covers entry-level operations, specifically
systems where treatment is limited to disinfection or groundwater systems not under
direct influence of surface water (GWUDI) without additional treatment. Option A
describes Class C and higher surface water treatment. Options C and D describe
advanced treatment requiring Class B or A certification. Class D operators must
recognize their operational boundaries under 30 TAC Chapter 30, Subchapter K.
3. Which of the following waterborne diseases is MOST commonly associated with
inadequate disinfection of drinking water and is caused by the protozoan Giardia
lamblia?
A. Hepatitis A
B. Giardiasis
C. Legionellosis
D. Cryptosporidiosis
,Correct Answer: B. Giardiasis
Rationale: Giardia lamblia (also Giardia intestinalis) causes giardiasis, a gastrointestinal
illness frequently linked to inadequate surface water treatment or disinfection failure.
Option A is viral. Option C is caused by Legionella pneumophila, typically associated with
building plumbing systems and warm water aerosols, not primarily inadequate primary
disinfection. Option D is caused by Cryptosporidium, which is highly chlorine-resistant
and requires filtration or UV for effective removal, making it less directly associated with
simple disinfection inadequacy than Giardia.
4. Under the federal Safe Drinking Water Act and TCEQ rules, a public water system
must provide a Consumer Confidence Report (CCR) to its customers no later than which
date annually?
A. January 1
B. April 1
C. July 1
D. October 1
Correct Answer: C. July 1
Rationale: The CCR must be delivered to customers by July 1 of each year, covering data
from the previous calendar year. This deadline is mandated by 40 CFR §141.155 and
adopted by reference in TCEQ rules. Option A is incorrect. Option B is the deadline for
systems on quarterly monitoring to submit compliance samples. Option D is beyond the
regulatory deadline and would constitute a violation.
, 5. A public water system in Texas is classified as a "community water system" if it
serves at least how many persons year-round?
A. 10 persons
B. 15 service connections
C. 25 persons
D. 50 persons
Correct Answer: C. 25 persons
Rationale: Per 30 TAC §290.38(32), a community water system serves at least 25
persons year-round or has at least 15 service connections. However, the question asks
for the person threshold, which is 25. Option A is below the threshold. Option B
describes the service connection threshold, not persons. Option D exceeds the
minimum requirement. Both 15 connections OR 25 persons define the classification.
6. Which physical characteristic of water is MOST directly responsible for causing
corrosion in distribution system pipes when elevated?
A. Turbidity
B. pH
C. Temperature
D. Color
Correct Answer: B. pH
