CWS CWS Hardness, Scale & Corrosion Control 1 — Questions and Answers
Question 1: What is the primary cause of scale deposits in water heaters and pipes in the US?
- High dissolved oxygen
- High total dissolved solids
- Calcium and magnesium carbonate precipitation (Correct answer)
- Elevated chlorine levels
Correct answer: Calcium and magnesium carbonate precipitation
Calcium and magnesium carbonates precipitate out of hard water when heated, forming the hard scale deposits seen in water heaters and pipes.
Question 2: The Langelier Saturation Index (LSI) is used to predict water's tendency to:
- Filter sediment
- Form scale or corrode pipes (Correct answer)
- Remove chlorine
- Soften water
Correct answer: Form scale or corrode pipes
The LSI measures the saturation level of calcium carbonate in water; a positive value indicates scale-forming tendency and a negative value indicates corrosive tendency.
Question 3: At what LSI value is water considered balanced (neither scale-forming nor corrosive)?
- LSI = -1.0
- LSI = 0 (Correct answer)
- LSI = +1.0
- LSI = +2.0
Correct answer: LSI = 0
An LSI of 0 indicates water is in equilibrium with calcium carbonate, meaning it is neither scale-forming nor corrosive.
Question 4: Which water condition is most likely to cause red staining on fixtures and laundry?
- High hardness
- High iron content (Correct answer)
- High manganese
- High sulfates
Correct answer: High iron content
Dissolved ferrous iron oxidizes to ferric iron upon exposure to air, depositing reddish-brown stains on fixtures, laundry, and plumbing.
Question 5: Galvanic corrosion in plumbing is most likely to occur when:
- Water is too soft
- Two dissimilar metals are in direct contact in the presence of water (Correct answer)
- Water temperature is below 50°F
- Chlorine residual exceeds 1 ppm
Correct answer: Two dissimilar metals are in direct contact in the presence of water
Galvanic corrosion occurs when two dissimilar metals form an electrochemical cell in the presence of an electrolyte such as water, causing the more anodic metal to corrode.
Question 6: A customer reports blue-green staining on their copper fixtures. This most likely indicates:
- High manganese
- Low pH corrosive water attacking copper pipes (Correct answer)
- High hardness
- Excessive chlorine
Correct answer: Low pH corrosive water attacking copper pipes
Low pH (acidic) water leaches copper from pipes, and the resulting copper dissolved in water leaves characteristic blue-green stains on fixtures and sinks.
CWS CWS Hardness, Scale & Corrosion Control 1
What is the primary cause of scale deposits in water heaters and pipes in the US?