Texas Class D Water License Exam
Questions And Answers - 40 Questions
Question 1: What is the primary purpose of coagulation
in water treatment?
A) To kill bacteria and viruses B) To remove dissolved gases C) To destabilize particles so they
can clump together D) To adjust pH levels
Answer: C) To destabilize particles so they can clump together
Rationale: Coagulation uses chemicals like aluminum sulfate or ferric chloride to neutralize the
negative charges on particles, allowing them to stick together and form larger flocs that can be
more easily removed through sedimentation and filtration.
Question 2: Which chemical is commonly used for
disinfection in public water systems?
A) Aluminum sulfate B) Sodium hypochlorite C) Ferric chloride D) Lime
Answer: B) Sodium hypochlorite
Rationale: Sodium hypochlorite (liquid bleach) is one of the most common disinfectants used in
water treatment. It effectively kills bacteria, viruses, and other pathogens. The other chemicals
listed are used for coagulation (A, C) or pH adjustment (D).
Question 3: What does turbidity measure in water?
A) The amount of dissolved solids B) The clarity or cloudiness of water C) The pH level D) The
temperature
Answer: B) The clarity or cloudiness of water
Rationale: Turbidity measures how clear or cloudy water appears by measuring the scattering
of light through the water. High turbidity indicates the presence of suspended particles that
make water appear cloudy or murky.
, Question 4: What is the maximum allowable turbidity
level for filtered water according to EPA standards?
A) 0.3 NTU B) 1.0 NTU C) 4.0 NTU D) 10.0 NTU
Answer: A) 0.3 NTU
Rationale: The EPA Surface Water Treatment Rule requires that filtered water not exceed 0.3
NTU (Nephelometric Turbidity Units) in 95% of measurements each month, with no single
measurement exceeding 1.0 NTU.
Question 5: Which process removes hardness from
water?
A) Chlorination B) Aeration C) Ion exchange D) Sedimentation
Answer: C) Ion exchange
Rationale: Ion exchange removes hardness by replacing calcium and magnesium ions (which
cause hardness) with sodium ions. This is also called water softening. The other processes
serve different purposes in water treatment.
Question 6: What type of bacteria is used as an indicator
of fecal contamination?
A) Streptococcus B) E. coli C) Salmonella D) Legionella
Answer: B) E. coli
Rationale: E. coli is the primary bacterial indicator used to detect fecal contamination in water
systems because it is naturally present in human and animal intestines and indicates the
possible presence of disease-causing organisms.
Question 7: What is the purpose of fluoridation in public
water supplies?
A) To improve taste B) To prevent tooth decay C) To kill bacteria D) To reduce corrosion
Questions And Answers - 40 Questions
Question 1: What is the primary purpose of coagulation
in water treatment?
A) To kill bacteria and viruses B) To remove dissolved gases C) To destabilize particles so they
can clump together D) To adjust pH levels
Answer: C) To destabilize particles so they can clump together
Rationale: Coagulation uses chemicals like aluminum sulfate or ferric chloride to neutralize the
negative charges on particles, allowing them to stick together and form larger flocs that can be
more easily removed through sedimentation and filtration.
Question 2: Which chemical is commonly used for
disinfection in public water systems?
A) Aluminum sulfate B) Sodium hypochlorite C) Ferric chloride D) Lime
Answer: B) Sodium hypochlorite
Rationale: Sodium hypochlorite (liquid bleach) is one of the most common disinfectants used in
water treatment. It effectively kills bacteria, viruses, and other pathogens. The other chemicals
listed are used for coagulation (A, C) or pH adjustment (D).
Question 3: What does turbidity measure in water?
A) The amount of dissolved solids B) The clarity or cloudiness of water C) The pH level D) The
temperature
Answer: B) The clarity or cloudiness of water
Rationale: Turbidity measures how clear or cloudy water appears by measuring the scattering
of light through the water. High turbidity indicates the presence of suspended particles that
make water appear cloudy or murky.
, Question 4: What is the maximum allowable turbidity
level for filtered water according to EPA standards?
A) 0.3 NTU B) 1.0 NTU C) 4.0 NTU D) 10.0 NTU
Answer: A) 0.3 NTU
Rationale: The EPA Surface Water Treatment Rule requires that filtered water not exceed 0.3
NTU (Nephelometric Turbidity Units) in 95% of measurements each month, with no single
measurement exceeding 1.0 NTU.
Question 5: Which process removes hardness from
water?
A) Chlorination B) Aeration C) Ion exchange D) Sedimentation
Answer: C) Ion exchange
Rationale: Ion exchange removes hardness by replacing calcium and magnesium ions (which
cause hardness) with sodium ions. This is also called water softening. The other processes
serve different purposes in water treatment.
Question 6: What type of bacteria is used as an indicator
of fecal contamination?
A) Streptococcus B) E. coli C) Salmonella D) Legionella
Answer: B) E. coli
Rationale: E. coli is the primary bacterial indicator used to detect fecal contamination in water
systems because it is naturally present in human and animal intestines and indicates the
possible presence of disease-causing organisms.
Question 7: What is the purpose of fluoridation in public
water supplies?
A) To improve taste B) To prevent tooth decay C) To kill bacteria D) To reduce corrosion
