What Is the Resin Capacity of a Water Softener?

Resin Beads

• An ion exchange water softener's tank contains resin beads with sodium ions. As hard, untreated water flows through, the resin beads attract calcium and magnesium ions. The beads then exchange these hard mineral ions for sodium ions. When the resin beads become totally saturated with hard mineral ions, regeneration must occur. In this process, the machine forces a liquid containing brine solution through the tank. This solution envelops the resin beads in sodium ions, replacing the magnesium and calcium ions. Then a fresh water cycle forces the brine solution, full of these hard mineral ions, out of the tank through a discharge pipe.

Grain Capacity

• Water softeners are marketed as having specific grain systems. A typical 32,000-grain system should contain contain 1 cubic foot of the resin beads necessary for water softening. This translates to removing 32,000 grains of hardness per cubic foot of resin. However, these specifications meet laboratory conditions, not necessarily true performance conditions. In a controlled laboratory setting, water flow, pressure and temperature don't fluctuate, conditions that cannot be replicated by the water softener in your basement. This means a more realistic resin softening capacity is closer to 30,000 grains of hardness, or less, per cubic foot. The same ratio for capacity holds true of other sizes of water softeners.

Salt

• A more efficient way to calculate a water softener's capacity is by how much salt is needed for each regeneration to achieve the manufacturer's stated resin capacity. Many manufacturers list the amount of salt needed as grains per pound of salt. Unlike a laboratory test under controlled conditions, this calculation method shows the amount of salt used and the resulting softener capacity.

Resin Lifespan

• Most water softener resin beads last between 10 to 15 years before either bead or tank replacement is required. Since these ion exchange resin beads consist primarily of porous plastic, strong oxidants in the water system tend to corrode them, leading to a shorter useful working lifespan. Common strong oxidants include chlorine or chloramines. Since the resin beads generally have a long useful life, when replacement is needed you must decide whether to replace only the beads or invest in a new, up-to-date water softener.