Practice Test Geeks(CWS) Certified Water Specialist Practice Test
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Reverse Osmosis Systems Flashcards

7 cards from real CWS practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. What NSF/ANSI standard specifically covers RO drinking water treatment systems?

    Answer: NSF/ANSI 58

    NSF/ANSI 58 is the standard for reverse osmosis drinking water treatment systems, covering contaminant reduction claims and system integrity.

  2. A customer reports their RO water has a salty or chlorine taste immediately after the system is sanitized. What is the most likely cause?

    Answer: Residual sanitizing solution not fully flushed

    Residual sanitizer (bleach or other biocide) remaining in the system must be thoroughly flushed through several tank cycles before water is safe to drink.

  3. What is the maximum recommended total dissolved solids (TDS) in feedwater for a standard residential RO membrane?

    Answer: 2,000 mg/L

    Most residential RO membranes are rated for feedwater TDS up to 2,000 mg/L; above this, rejection rates decline and scaling risk increases significantly.

  4. Which contaminant is NOT effectively removed by standard residential RO membranes?

    Answer: Dissolved carbon dioxide (CO2)

    Dissolved CO2 is a small, uncharged gas molecule that passes freely through RO membranes and is not removed by the RO process.

  5. Why is the storage tank air pre-charge pressure important in a residential RO system?

    Answer: Both: it sets ASO valve shutoff pressure and maintains delivery flow

    Proper pre-charge pressure (typically 7-8 psi) ensures the bladder fully collapses during draw-down (delivery) and also sets the pressure at which the ASO valve shuts off production.

  6. A technician observes iron staining on an RO membrane after only 3 months of service. What pretreatment would prevent this?

    Answer: Oxidation filtration to remove iron before the membrane

    Dissolved iron must be oxidized and filtered before reaching the RO membrane to prevent iron fouling and membrane coloring.

  7. What is the recommended frequency for replacing the pre-filters (sediment and carbon) in a residential RO system under normal conditions?

    Answer: Every 6-12 months

    Pre-filters should typically be replaced every 6-12 months to protect the RO membrane from sediment and chlorine damage.