2025 Texas Class D Water License Exam | Study Guide and Practice Material

2025 Texas Class D Water License
Exam | Study Guide and Practice
Material


This exam consists of 100 multiple-choice questions designed to prepare candidates for the
2025/2026 Texas Class D Water Operator License Exam, administered by the Texas
Commission on Environmental Quality (TCEQ). The content aligns with TCEQ standards,
covering water treatment processes, safety procedures, disinfection methods, monitoring
requirements, and Texas regulatory standards, as outlined in 30 TAC Chapter 30, the Surface
Water Treatment Rule (SWTR), and OSHA guidelines. Each question includes four answer
options, the correct answer, and a detailed rationale citing relevant sources.



Question 1
What is the primary purpose of the water utility industry in Texas?
A) Maximize water sales
B) Deliver safe drinking water to consumers
C) Reduce water usage
D) Treat wastewater only

Correct Answer: B
Rationale : The primary purpose of the water utility industry is to produce and deliver safe
drinking water to consumers, meeting federal and state standards (30 TAC § 30.51). Sales (A),
usage reduction (C), and wastewater (D) are secondary or unrelated.



Question 2
The pH of water is expressed on a scale ranging from:
A) 0–7
B) 0–14
C) 1–7
D) 1–14

,Correct Answer: B
Rationale : The pH scale ranges from 0 (acidic) to 14 (basic), with 7 being neutral, used to
assess water quality (EPA Water Quality Standards, 2025). Other ranges (A, C, D) are incorrect.



Question 3
What is the minimum chlorine dosage for disinfecting a new water main?
A) 25 mg/L
B) 30 mg/L
C) 40 mg/L
D) 50 mg/L

Correct Answer: D
Rationale : TCEQ requires a minimum chlorine dosage of 50 mg/L for disinfecting new mains to
ensure pathogen elimination (30 TAC § 290.44). Lower dosages (A, B, C) are insufficient.



Question 4
A common chemical used for disinfecting small public water supplies is:
A) Soda ash
B) Sodium hypochlorite
C) Copper sulfate
D) Fluoride

Correct Answer: B
Rationale : Sodium hypochlorite is commonly used for disinfection in small water systems due
to its effectiveness against pathogens (TCEQ Water Treatment Guidelines, 2025). Soda ash (A)
adjusts pH, copper sulfate (C) controls algae, and fluoride (D) prevents tooth decay.



Question 5
What does aeration remove from water supplies?
A) Turbidity
B) Tastes, odors, and certain organics
C) Hardness
D) Chlorides

Correct Answer: B
Rationale : Aeration removes tastes, odors, and volatile organics by incorporating air into water
(TCEQ Treatment Standards, 2025). Turbidity (A) is removed by filtration, hardness (C) by
softening, and chlorides (D) by reverse osmosis.

, Question 6
Gravity filters primarily remove which of the following from surface water?
A) Nitrates
B) Turbidity
C) Hardness
D) Taste and odors

Correct Answer: B
Rationale : Gravity filters remove turbidity (suspended particles) from surface water (TCEQ
Filtration Guidelines, 2025). Nitrates (A) require ion exchange, hardness (C) softening, and odors
(D) aeration or carbon filtration.



Question 7
What is the purpose of a storage tank in a water system?
A) Treat water chemically
B) Equalize demand and provide disinfection time
C) Filter impurities
D) Cool water

Correct Answer: B
Rationale : Storage tanks equalize demand, provide water for firefighting, and allow time for
disinfection (TCEQ Water System Design, 2025). Treatment (A), filtration (C), and cooling (D)
are handled by other processes.



Question 8
What protects a well from surface contamination?
A) Aeration
B) Well casing and cementing
C) Chlorination
D) Filtration

Correct Answer: B
Rationale : Well casing and cementing prevent surface water contamination (30 TAC § 290.41).
Aeration (A) removes odors, chlorination (C) disinfects, and filtration (D) removes particles.



Question 9
What chemical is added to bacteriological sample bottles to dechlorinate water?
A) Sodium chloride
B) Sodium thiosulfate