WHAT MAKES WATER HARD?
AND HOW DOES IT BECOME SOFT?
As water flows through layers of rock underground, it picks up loose particles and dissolves minerals from its surroundings. Because of this characteristic and the kind of rock common in many aquifers, calcium and magnesium minerals are frequently found in household water. Water with substantial amounts of calcium and magnesium is referred to as "hard water."
Hard water minerals reduce water's ability to function effectively in our homes. For instance, bath soap combines with the minerals and forms a pasty scum that accumulates on the bathtubs and sinks. Homeowners must use more soap and detergent in washing, so expense for these products increases.
These minerals also combine with soap in the laundry, and the residue doesn't rinse well from fabric, leaving clothes dull. Hard water spots appear on everything that is washed in and around the home - from dishes and silverware to the family car.
Hard water not only affects household cleaning, but the minerals also can build up on the inside of pipes in the plumbing system. And in water heaters, the minerals settle on the heating element, the walls of the tank, in the hot water pipes, and in faucets where they produce a scale (similar to the original rock) that reduces the efficiency and life of the hot water system.
Water Softeners Make Water Work Better
Water softeners combat this nuisance by eliminating the minerals that cause hard water. The most common kind of water softener is a mechanical appliance plumbed directly into the home's water supply intake. (See Figure 1) The softener exchanges calcium and magnesium with sodium in a process called ion exchange.
The water softener system consists of a mineral tank and a brine tank. The water supply pipe is connected to the mineral tank so that water coming into the house must pass through the tank before it can be used.
The mineral tank holds small beads (also known as resin) that carry a negative electrical charge. The positively charged calcium and magnesium (called ions) are attracted to the negatively charged beads. This attraction makes the minerals stick to the beads as the hard water passes through the mineral tank. (See Figure 3)
Eventually the surfaces of the beads in the mineral tank become coated with the calcium and magnesium minerals. To clean the beads, a strong sodium (salt) solution held in the brine tank is flushed through the mineral tank. Sodium ions also have a positive electrical charge, just not quite as strong as that of calcium and magnesium. This large volume of sodium ions overpowers the calcium and magnesium ions and drives them off of the beads and into the solution. The sodium solution carrying the minerals is then drained out of the unit. Some sodium ions remain in the tank attached to the surfaces of the beads.
The Softening Process
The normal water softening cycle operates like this:
Hard water enters the mineral tank. Inside the tank, the calcium and magnesium ions carried in the water attach themselves to the beads. The surfaces of the beads eventually hold their limit of calcium and magnesium and can't remove anymore from the water. At this point the water softener must be "regenerated." (See Figure 2) The three-step regeneration cycle can be scheduled according to a timer or by a flow detection meter. The first step, called the backwash phase, reverses the water's flow and flushes any accumulated dirt particles out of the tank and down the drain. Next, the regeneration or recharge phase, the sodium rich brine solution flows from the brine tank into and through the mineral tank. The brine washes the calcium and magnesium off the beads. In the final phase, the mineral tank is flushed of the excess brine, which now also holds the calcium and magnesium, and the solution is disposed of down the drain.
Sodium ions from the previous regeneration cycle cling to the beads. Now when the hard water flows into the mineral tank, the calcium and magnesium ions change places with the sodium ions on the resin. The displaced sodium ions remain dissolved in the water.
