Water Softening & Ion Exchange 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.
Read the first 7 Water Softening & Ion Exchange flashcards as text
A household uses 300 gallons per day and the raw water hardness is 20 grains per gallon (gpg). What is the daily softening requirement?
Answer: 6,000 grains
Daily softening requirement = daily water use × hardness = 300 gal/day × 20 gpg = 6,000 grains per day.
A water softener is rated at 30,000 grains capacity. If the household daily softening requirement is 6,000 grains, how many days will the softener serve between regenerations (at 100% capacity use)?
Answer: 5 days
Days between regenerations = total capacity ÷ daily requirement = 30,000 ÷ 6,000 = 5 days.
What effect does excessively high service flow rate have on a water softener's performance?
Answer: It causes incomplete exchange and early hardness breakthrough
At excessive flow rates, water moves through the bed too quickly for complete ion exchange, causing early hardness leakage before the rated capacity is reached.
Iron fouling of softener resin is most likely to occur when:
Answer: Iron concentration in raw water exceeds 0.5 mg/L and the softener is not regenerated frequently enough
Soluble ferrous iron can be softened at low levels, but when it oxidizes to insoluble ferric iron on the resin, it fouls exchange sites and reduces capacity permanently if not treated.
What is 'hardness leakage' in a water softener?
Answer: A measurable concentration of hardness ions in the softener effluent during normal service
Hardness leakage is a small but detectable amount of Ca²⁺ and Mg²⁺ that passes through the softener in the effluent, caused by incomplete regeneration or kinetic limitations.
Which condition would indicate that a softener's resin bed may need to be replaced rather than simply cleaned?
Answer: Resin volume has decreased by 30% or more due to attrition and fines loss
A significant reduction in resin volume (typically >20–30%) due to bead breakage and loss of fines means the bed has lost substantial exchange capacity and replacement is warranted.
A timer-initiated softener regenerates based on:
Answer: A preset time schedule regardless of water consumption
Timer-based control initiates regeneration at a fixed interval (e.g., every 3 days) regardless of how much water was actually used, which can waste salt or deliver hard water.