Drinking water systems and definitions practice questions
20 free practice questions from 40 CFR Part 141 Subpart A. Each answer is explained and linked to the rule it comes from.
Drinking water systems and definitions
20 questions across 6 topics. After each answer you see why it is right, with a link to the official source.
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Scope and coverage
1. A system has only distribution and storage facilities, buys all of its water from a regulated public water system that does not own or operate it, and is not a carrier that conveys passengers in interstate commerce. Under 141.3, which added fact would make Part 141 apply to it?
- A. It stores the water in an elevated tank
- B. It sells water to the people it serves
- C. It has no collection or treatment facilities
- D. It gets all of its water from a public water system to which the regulations apply
Show answer
Answer: B. It sells water to the people it serves
Part 141 applies "unless the public water system meets all of the following conditions", one of which is that it "Does not sell water to any person". Selling water means it no longer meets every condition.
2. A system delivers water through a constructed conveyance other than a pipe. Under the 141.2 definition of "service connection", which listed condition keeps a connection to that system from counting as a service connection?
- A. The water is used for drinking without any treatment
- B. The connection serves fewer than 25 people
- C. The water is used exclusively for purposes other than residential uses (drinking, bathing, cooking or similar uses)
- D. The connection was made before August 5, 1998
Show answer
Answer: C. The water is used exclusively for purposes other than residential uses (drinking, bathing, cooking or similar uses)
Service connection "does not include a connection to a system that delivers water by a constructed conveyance other than a pipe if" one of three conditions is met, the first being "(1) The water is used exclusively for purposes other than residential uses (consisting of drinking, bathing, and cooking, or other similar uses)".
3. Which facilities outside the operator's control does the 141.2 public water system definition still include in the system?
- A. Collection or pretreatment storage facilities used primarily in connection with the system
- B. Distribution mains owned by the customers
- C. Any special irrigation district that supplies the system
- D. The plumbing inside each customer's building
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Answer: A. Collection or pretreatment storage facilities used primarily in connection with the system
The term includes "any collection or pretreatment storage facilities not under such control which are used primarily in connection with such system." Special irrigation districts are excluded from the term.
System types and responsible parties
4. Town B's public water system runs year-round, treats no water itself and buys all of its finished water from City A's public water system through a direct connection. Which 141.2 term describes Town B's system?
- A. A wholesale system
- B. A seasonal system
- C. A special irrigation district
- D. A consecutive system
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Answer: D. A consecutive system
A consecutive system "is a public water system that receives some or all of its finished water from one or more wholesale systems." A wholesale system is the one that "treats source water as necessary to produce finished water and then delivers some or all of that finished water to another public water system."
5. A summer camp's non-community water system is shut down every fall and started up again each spring, and it is not run as a public water system the rest of the year. Which 141.2 term covers it?
- A. A seasonal system
- B. A consecutive system
- C. A wholesale system
- D. A community water system
Show answer
Answer: A. A seasonal system
A seasonal system "is a non-community water system that is not operated as a public water system on a year-round basis and starts up and shuts down at the beginning and end of each operating season."
6. A city owns a public water system and has hired a private company to run it day to day. Under the 141.2 definitions, which of them is a "supplier of water"?
- A. Only the city, because it owns the system
- B. Only the company, because it operates the system
- C. Both the city and the company
- D. Neither; the State with primary enforcement responsibility is the supplier of water
Show answer
Answer: C. Both the city and the company
Supplier of water "means any person who owns or operates a public water system." Person "means an individual; corporation; company; association; partnership; municipality; or State, Federal, or tribal agency", so the owning city and the operating company both qualify.
7. A system's only source is a well that the State has determined is ground water under the direct influence of surface water, and the system is subject to subpart H. How does 141.2 classify it?
- A. As a subpart H system, because GWUDI counts the same as surface water for that term
- B. As a ground water system only, because subpart H systems use surface water alone
- C. As a subpart H system only if it serves more than 10,000 persons
- D. As a subpart H system only if it is a community water system
Show answer
Answer: A. As a subpart H system, because GWUDI counts the same as surface water for that term
Subpart H systems are "public water systems using surface water or ground water under the direct influence of surface water as a source that are subject to the requirements of subpart H of this part."
Water sources
8. Under the 141.2 definition of ground water under the direct influence of surface water (GWUDI), what may the State's determination of direct influence be based on?
- A. The number of service connections the well supplies
- B. The certification grade of the system's operator
- C. The volume of water the well pumps each day
- D. Site-specific measurements of water quality and/or documentation of well construction characteristics and geology with field evaluation
Show answer
Answer: D. Site-specific measurements of water quality and/or documentation of well construction characteristics and geology with field evaluation
Direct influence is determined for individual sources under State criteria, and "The State determination of direct influence may be based on site-specific measurements of water quality and/or documentation of well construction characteristics and geology with field evaluation."
9. After each heavy rain, a well's turbidity and temperature shift quickly and closely track a nearby river. Which element of the 141.2 GWUDI definition does this observation match?
- A. Significant occurrence of insects or other macroorganisms
- B. Significant and relatively rapid shifts in water characteristics that closely correlate to climatological or surface water conditions
- C. Water that is open to the atmosphere and subject to surface runoff
- D. Water introduced into the distribution system without further treatment
Show answer
Answer: B. Significant and relatively rapid shifts in water characteristics that closely correlate to climatological or surface water conditions
GWUDI includes ground water with "significant and relatively rapid shifts in water characteristics such as turbidity, temperature, conductivity, or pH which closely correlate to climatological or surface water conditions."
Standards and goals
10. Notwithstanding the MRDLs in 141.65, the 141.2 MRDL definition lets operators raise residual disinfectant levels in the distribution system for a time to address specific microbiological contamination problems. Which disinfectants does that allowance cover?
- A. Chlorine dioxide only
- B. Chlorine or chloramines, but not chlorine dioxide
- C. Chlorine, chloramines and chlorine dioxide
- D. Ozone only
Show answer
Answer: B. Chlorine or chloramines, but not chlorine dioxide
"Notwithstanding the MRDLs listed in § 141.65, operators may increase residual disinfectant levels of chlorine or chloramines (but not chlorine dioxide) in the distribution system to a level and for a time necessary to protect public health".
11. According to the 141.2 definition of maximum residual disinfectant level goal (MRDLG), what do MRDLGs not reflect?
- A. An adequate margin of safety
- B. Known or anticipated adverse effects on the health of persons
- C. The level of a disinfectant added for water treatment
- D. The benefit of the addition of the chemical for control of waterborne microbial contaminants
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Answer: D. The benefit of the addition of the chemical for control of waterborne microbial contaminants
"MRDLGs are nonenforceable health goals and do not reflect the benefit of the addition of the chemical for control of waterborne microbial contaminants." The definition itself is built on the level "at which no known or anticipated adverse effect on the health of persons would occur, and which allows an adequate margin of safety."
12. For chlorine dioxide, what compliance basis does the 141.2 MRDL definition set?
- A. A running annual average of monthly averages of distribution system samples, computed quarterly
- B. A locational running annual average at each monitoring location
- C. Daily samples at the entrance to the distribution system, with no two consecutive daily samples above the MRDL
- D. One sample per month at the tap of the first customer
Show answer
Answer: C. Daily samples at the entrance to the distribution system, with no two consecutive daily samples above the MRDL
"For chlorine dioxide, a PWS is in compliance with the MRDL when daily samples are taken at the entrance to the distribution system and no two consecutive daily samples exceed the MRDL." The running annual average basis is the one stated for chlorine and chloramines.
13. The 141.2 text states the lead and copper action levels as revised in 2024 (Subpart I compliance required by November 1, 2027). For what purpose does 141.2 define the term "action level"?
- A. For every contaminant that has an MCL in subpart G
- B. For subpart I only, as the lead or copper concentrations that determine requirements under that subpart
- C. For disinfectant levels at the consumer's tap
- D. For the secondary standards in Part 143
Show answer
Answer: B. For subpart I only, as the lead or copper concentrations that determine requirements under that subpart
"Action level, for the purpose of subpart I of this part only, means the concentrations of lead or copper in water as specified in § 141.80(c) which determines requirements under subpart I of this part."
Treatment and monitoring terms
14. How does 141.2 decide which service connections are "near the first service connection"?
- A. The 20 percent of all service connections nearest the treatment facility, measured by water transport time
- B. The 10 service connections closest to the treatment facility by straight-line distance
- C. The 20 percent of service connections with the shortest pipe length from the plant
- D. Any service connection within one mile of the treatment facility
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Answer: A. The 20 percent of all service connections nearest the treatment facility, measured by water transport time
It means "at one of the 20 percent of all service connections in the entire system that are nearest the water supply treatment facility, as measured by water transport time within the distribution system."
15. Which dates does 141.2 give for the third calendar year compliance cycle?
- A. January 1, 1993 to December 31, 2001
- B. January 1, 2002 to December 31, 2010
- C. January 1, 2011 to December 31, 2019
- D. January 1, 2020 to December 31, 2028
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Answer: C. January 1, 2011 to December 31, 2019
"The first calendar year cycle begins January 1, 1993 and ends December 31, 2001; the second begins January 1, 2002 and ends December 31, 2010; the third begins January 1, 2011 and ends December 31, 2019."
16. A reservoir stores finished water that gets no further treatment to reduce microbial pathogens except residual disinfection, and it is directly open to the atmosphere. Which 141.2 term fits it?
- A. Presedimentation
- B. Plant intake
- C. Combined distribution system
- D. Uncovered finished water storage facility
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Answer: D. Uncovered finished water storage facility
An uncovered finished water storage facility "is a tank, reservoir, or other facility used to store water that will undergo no further treatment to reduce microbial pathogens except residual disinfection and is directly open to the atmosphere."
Variances, siting and effective dates
17. Which contaminant's MCL does 141.4(a) name as one from which variances or exemptions may not be granted?
- A. E. coli
- B. Arsenic
- C. Fluoride
- D. Nitrite
Show answer
Answer: A. E. coli
Variances or exemptions may be granted, "except that variances or exemptions from the MCLs for total coliforms and E. coli and variances from any of the treatment technique requirements of subpart H of this part may not be granted."
Source: eCFR: 40 CFR 141.4, Variances and exemptions (as of Nov 3, 2026)
18. Under 141.5, what must a person do before entering into a financial commitment for, or starting construction of, a new public water system?
- A. Get a construction permit from the EPA Administrator
- B. Notify the system's future customers in writing
- C. File a report with EPA within 30 days after construction ends
- D. Notify the State and, to the extent practicable, avoid sites with the risks the section lists
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Answer: D. Notify the State and, to the extent practicable, avoid sites with the risks the section lists
Before that step "he shall notify the State and, to the extent practicable, avoid locating part or all of the new or expanded facility at a site which" has the listed risks.
Source: eCFR: 40 CFR 141.5, Siting requirements (as of Nov 3, 2026)
19. Which part of a facility does 141.5(b) leave out of the siting criterion about the floodplain of a 100-year flood?
- A. Storage tanks
- B. Treatment buildings
- C. Intake structures
- D. Pumping stations
Show answer
Answer: C. Intake structures
141.5(b) lists a site that, "Except for intake structures, is within the floodplain of a 100-year flood or is lower than any recorded high tide where appropriate records exist."
Source: eCFR: 40 CFR 141.5, Siting requirements (as of Nov 3, 2026)
20. What compliance date does 141.6(l) give for the PFAS MCLs in 141.61?
- A. June 25, 2024
- B. April 26, 2029
- C. April 26, 2027
- D. January 23, 2006
Show answer
Answer: B. April 26, 2029
"The compliance date for the PFAS MCLs in § 141.61, as specified in § 141.60, and for § 141.203 notifications of violations of the PFAS MCLs is April 26, 2029." June 25, 2024 is the effective date and April 26, 2027 the reporting compliance date.
Source: eCFR: 40 CFR 141.6, Effective dates (as of Nov 3, 2026)