CWS Residential Water Quality Testing 2 — Questions and Answers
Question 1: Which parameter is MOST commonly tested to assess microbiological safety in residential well water?
- Total dissolved solids (TDS)
- Total coliform bacteria (Correct answer)
- Hardness as CaCO3
- Chlorine residual
Correct answer: Total coliform bacteria
Total coliform bacteria is the primary indicator organism used to assess microbiological contamination in well water.
Question 2: A homeowner's water test shows a pH of 6.1. Which problem is MOST likely associated with this result?
- Scale buildup in pipes
- Corrosion of copper plumbing (Correct answer)
- Taste of chlorine
- High bacterial count
Correct answer: Corrosion of copper plumbing
A pH of 6.1 is acidic and promotes corrosion of copper and other metal plumbing components.
Question 3: What is the EPA's Maximum Contaminant Level (MCL) for nitrate in drinking water, expressed as nitrogen?
- 5 mg/L
- 10 mg/L (Correct answer)
- 15 mg/L
- 25 mg/L
Correct answer: 10 mg/L
The EPA MCL for nitrate (as nitrogen) is 10 mg/L, primarily to protect infants from methemoglobinemia.
Question 4: Which test method is used to detect E. coli specifically in water samples?
- Heterotrophic plate count (HPC)
- Most probable number (MPN) with confirmatory testing (Correct answer)
- Turbidity measurement
- Conductivity analysis
Correct answer: Most probable number (MPN) with confirmatory testing
The MPN method with confirmatory testing (or membrane filtration) differentiates E. coli from other coliforms using enzyme-based substrates.
Question 5: A water sample collected in a sterile bottle is held at room temperature for 48 hours before testing. How does this affect coliform results?
- Results will be unaffected
- Coliform counts may be falsely elevated (Correct answer)
- Coliform counts will be falsely low
- Only E. coli counts increase
Correct answer: Coliform counts may be falsely elevated
Warm holding temperatures allow bacteria to multiply, potentially producing falsely elevated coliform counts.
Question 6: Which type of residential water sample is submitted in a sodium thiosulfate-treated bottle?
- Metals analysis sample
- Bacteriological sample from a chlorinated source (Correct answer)
- Nitrate sample
- Hardness sample
Correct answer: Bacteriological sample from a chlorinated source
Sodium thiosulfate neutralizes residual chlorine, preventing it from killing bacteria during transit to the lab.
Question 7: What does a turbidity reading of 5 NTU in untreated well water MOST likely indicate?
- High iron content only
- Possible sediment, microorganisms, or surface water intrusion (Correct answer)
- Excessive hardness
- High total dissolved solids
Correct answer: Possible sediment, microorganisms, or surface water intrusion
Elevated turbidity in well water suggests suspended particles, which may include sediment, microorganisms, or infiltration of surface water.
CWS Residential Water Quality Testing 2
Which parameter is MOST commonly tested to assess microbiological safety in residential well water?