Mixed Deck — All CWS Topics Flashcards

An acid neutralizer using calcite media is sized for a 10 gpm service flow. To prevent calcite loss during backwash, what maximum backwash rate is typically specified?

Answer: 5 gpm per square foot of bed area

Calcite backwash rates are typically kept at or below 5 gpm/ft² to achieve bed expansion without washing calcite particles out of the tank.

What is a common pitfall when implementing ultraviolet disinfection systems practices?

Answer: Failing to adapt approaches to specific contexts while maintaining core principles

A common pitfall is either rigidly following templates without adaptation or ignoring core principles entirely, rather than finding the right balance.

A carbon filter is being designed to reduce chlorine from municipal water at a service flow rate of 8 gpm. The empty bed contact time (EBCT) required is 5 minutes. What minimum volume of carbon is needed?

Answer: 1.6 cubic feet

EBCT = bed volume (ft³) / flow rate (gpm); rearranged: volume = 8 gpm × 5 min = 40 gallons ≈ 5.35 ft³, but converting gpm to gal/min keeps it simple: 8 gpm × 5 min / 7.48 gal/ft³ ≈ 5.35 ft³.

Which characteristic is described by the 'uniformity coefficient' (UC) of a filter media?

Answer: The ratio of the d60 to d10 particle sizes

The uniformity coefficient is d60/d10, where d60 is the sieve size passing 60% of the media and d10 is the effective size; a lower UC indicates a more uniform particle distribution.

Which of the following contaminants is BEST addressed by a POE system rather than a POU system?

Answer: Hydrogen sulfide causing odor from all hot and cold faucets

Hydrogen sulfide that affects all fixtures—including showers where inhalation is a concern—warrants a whole-house POE treatment solution.

Which water quality parameter, if elevated, most reduces UV system effectiveness by absorbing UV light before it reaches pathogens?

Answer: Color and dissolved organic carbon (DOC)

Dissolved organic carbon, tannins, and color compounds absorb UV at 254 nm, lowering UVT and reducing germicidal dose delivered to microorganisms.

Which regulatory document provides the primary US guidance for UV disinfection of drinking water at large surface water systems?

Answer: USEPA UV Disinfection Guidance Manual (UVDGM), 2006

The USEPA UVDGM (2006) provides comprehensive guidance on reactor validation, dose monitoring, and operational requirements for compliance under the LT2ESWTR.

Which type of RO membrane configuration is most commonly used in residential point-of-use systems?

Answer: Spiral-wound

Spiral-wound membranes are the dominant configuration for residential RO because they pack a large membrane surface area into a compact cylindrical housing at low cost.

A customer wants to remove fluoride from their drinking water. Which treatment technology is specifically effective for fluoride reduction?

Answer: Reverse osmosis system or activated alumina filter

Reverse osmosis and activated alumina are among the few technologies that effectively reduce fluoride levels in drinking water.

What is the primary reason a water treatment system installed on a well should include a check valve between the pump and the pressure tank?

Answer: To stop backflow of water into the well when the pump shuts off

A check valve prevents pressurized water from flowing back down into the well casing when the pump stops, protecting both the pump and maintaining system pressure.

What is the primary purpose of conducting a hardness test during an in-home water assessment?

Answer: To determine if a water softener or scale inhibitor is warranted and to properly size the resin capacity

Hardness testing provides the grain-per-gallon data needed to size a softener correctly and justify the purchase.

When a water softener is sold to a tenant (not the property owner), which additional documentation step is most important?

Answer: Obtaining written authorization from the property owner before installation

Installing equipment on a property owned by someone else requires written authorization from the property owner to avoid liability and ensure a valid installation agreement.

When implementing filtration media & technologies practices, what should CWS professionals prioritize?

Answer: Alignment with professional standards, stakeholder needs, and organizational goals

Effective implementation of filtration media & technologies requires balancing professional standards, stakeholder needs, and organizational objectives for optimal results.

What is the recommended maximum SDI (Silt Density Index) value for feedwater entering most RO systems?

Answer: SDI < 5

An SDI of less than 5 is generally required to protect RO membranes from excessive particulate fouling.

In a whole-house sediment filtration system, which filter media configuration is called a 'multi-media' or 'multimedia' filter?

Answer: Layered beds of anthracite coal, sand, and garnet arranged by density

Multimedia filters use layered beds — typically anthracite on top, silica sand in the middle, and garnet on the bottom — allowing filtration from coarse to fine throughout the bed depth.

Potassium permanganate (KMnO4) is used in water treatment primarily to:

Answer: Oxidize iron, manganese, and hydrogen sulfide

Potassium permanganate is a strong oxidizer that converts dissolved iron, manganese, and hydrogen sulfide into filterable precipitates.

Which oxidation method is most commonly used to convert dissolved ferrous iron to filterable ferric iron?

Answer: Aeration

Aeration exposes water to oxygen, converting soluble ferrous iron into insoluble ferric iron that can then be filtered.

Which closing technique involves offering the customer a choice between two options, both of which result in a sale?

Answer: Alternative choice close

The alternative choice close (e.g., 'Would you prefer the whole-house system or the point-of-use unit?') narrows the decision to which product, not whether to buy.

Which item is most important to record on every service call to support future warranty or liability claims?

Answer: Date, technician name, work performed, parts replaced, and post-service water test results

A complete service record including date, technician, work performed, parts used, and post-service test data creates a defensible record for warranty and liability purposes.

When a UV system alarm indicates low UV intensity, what is the FIRST corrective action a CWS operator should take before assuming lamp failure?

Answer: Inspect and clean the quartz sleeve, then verify UVT and sensor calibration before replacing the lamp

Sleeve fouling and sensor drift are far more common causes of low-intensity alarms than lamp failure; cleaning and recalibrating should be verified first to avoid unnecessary lamp replacement costs.