Hardness Removal Efficiency and Leakage

Removal efficiency is the honest way to grade a softener, because "soft water" is a marketing word and 1 gpg out of 20 gpg is not the same thing as 0.1 out of 20. Subtract the outlet from the inlet, divide by the inlet, and you have the fraction removed; whatever is left is leakage. A bed taking 20 gpg down to 1 gpg is running 95% removal and 5% leakage — acceptable for a house, unacceptable ahead of a low-pressure steam boiler, where the specification is typically under 1 mg/L as CaCO₃, or better than 99.7% on the same water.

Leakage is not random; it comes from the bottom of the resin column. During regeneration the brine flows counter-current or co-current through the bed, and whatever calcium is left on the last few inches of resin is what the service water meets on its way out. Low salt doses leave more of it, high flow rates give less contact time to strip it, and high inlet TDS makes sodium a less effective competitor for the exchange sites. If a customer complains that their new softener "doesn't feel soft," measure the outlet hardness before touching anything: 3 gpg leaking through a system that should deliver 0.2 usually means a low salt setting, a bridged brine tank, or a bed that has channelled and needs a manual backwash.