How to choose a water softener

The inner workings of a water softener are surprisingly simple. Sodium from the brine tank clings to the plastic beads in the mineral tank, and when hard water from the supply enters the mineral tank, sodium is released into the water system and the hard minerals then cling to the beads.

Hard water contains calcium, magnesium and other dissolved minerals. While it is safe to drink, it leaves stains on sinks, showers and toilet bowls.

It also reduces the cleaning power of soaps and detergents, causes scale buildup in faucets and pipes, and can reduce the efficiency and shorten the lifespan of water heaters and appliances.

How a water softener works

All water softeners operate on the same principle, trade hard minerals for something else (typically sodium) in a process called ion exchange. The heart of a water softener is the mineral tank, which is filled with small polystyrene beads often called resin or zeolite.

These beads carry a negative ionic charge. Calcium and magnesium both carry positive ionic charges, so they will cling to the beads as water passes through the mineral tank.

Sodium ions also carry a positive charge, although not as strong as calcium and magnesium. When a very strong brine solution is flushed through a tank that has been saturated with calcium and magnesium, the large volume of sodium ions is enough to drive the calcium and magnesium ions off the beads.

Most water softeners have a separate brine tank that uses common salt pellets to create this brine solution, although many newer softeners house both the mineral tank and brine tank within one unit, creating a smaller footprint where it is to be installed.

During typical operation, hard water moves into the mineral tank and the calcium and magnesium ions cling to the beads, replacing the sodium ions, which go into the home’s water supply.

When the beads become saturated with calcium and magnesium, the unit then enters a three-phase regenerating cycle. First, the backwash phase reverses water flow to flush dirt out of the tank. Second, the recharge phase carries the concentrated sodium solution from the brine tank into the mineral tank, which trades the calcium and magnesium ions for sodium ions. Third, the flush phase rids the mineral tank of excess brine and refills the brine tank.

How to choose a water softener

The water softener you install should be sized by the number of grains of hardness it can remove from water between regenerations: small units are typically sized at 12,000-16,000 grains, medium units handle from 20,000-40,000 grains, and large units are typically sized at 40,000 grains plus. Ideally you want to choose a water softener that can go at least three days between recharges.

A basic formula for calculating softener size is to multiply the number of people in a household by 75 (the average number of gallons used per person per day). This number can obviously vary widely depending on a particular family’s water-use habits, but this is a good average starting point.

You then multiply that number by the water’s hardness – the grains per gallon (GPG) figure provided by a water test. Then factor in the three-day regeneration to determine the capacity needed.

For example, a family of five uses 375 gallons of water per day (5 x 75), and if the water has a 10 GPG rating, that family needs to remove 3,750 GPG per day. Multiply 3,750 by three (representing regeneration every three days) and that family would require a water softener sized for at least 11,250 grains.

Regeneration is typically controlled in one of three different ways: timers, meters and manually.

• Timer-regenerated softeners regenerate once every set period (every seven days, for example), and no matter how much water is used during that period, the unit will regenerate and use about 8 pounds of salt each time. This system is a little cheaper than metered, but salt usage is high.
• Meter-regenerated systems keep track of how much water is actually used and regenerates only when necessary. This system is more expensive, but is also the most popular.
• Manually regenerated systems are best suited areas where no drain is available. A garden hose is used to drain the unit outside when regeneration is necessary. For this type, larger capacity systems are desirable.

—By Rob Fanjoy