Water Softener 101. How Softeners Work.
Water Softeners
The following is intended as an introduction to water softeners. It is not the final word. There are exceptions and enhancements that apply to most of the statements made below, so read it with a grain of salt. (Softener salt, of course.)
What is "Hard Water"?
“Hard” water is water that has an excessive amount of the minerals calcium and magnesium. These minerals prevent soap from lathering, interfere with water’s effectiveness as a cleaning agent, cause spotting on dishes and appliances, and, most especially, form a hard, damaging scale buildup in pipes and on fixtures than shortens their life and decreases their efficiency, and makes them unattractive.
What is a Water Softener?
A water softener is a device that removes calcium and magnesium from water and prevents the bad effects of hard water.
Softeners normally consist of three parts: a brine tank that holds salt, a mineral tank that holds treatment resin, and a control valve that sits on top of the mineral tank and directs the operation of softening the water and sending it to the home. See the illustration above.
A water softener is not a filter. It is an ion exchanger. It works by exchanging sodium ions for calcium and magnesium ions. When water passes through the treatment bed of the water softener, the hardness minerals leave the water and are replaced by sodium.
Softened water, therefore, has a sodium content that is equal to or higher than the hardness mineral content of the untreated water. Calcium and magnesium have been "exchanged" for sodium.
Measuring Hardness. What is a “grain”?
Minerals in water are usually measured in ppm (parts per million) or mg/L (milligrams per liter). Ppm and mg/L represent the same amount. 200 ppm = 200 mg/L. City water departments usually report hardness in ppm or mg/L.
Water treatment professionals usually measure hardness in “grains per gallon.” A grain is 17.1 ppm or 17.1 mg/L. You arrive at grains per gallon by dividing 17.1 into ppm or mg/l. Thus, water with 200 mg/L hardness has about 11.6 grains per gallon of hardness.Water that has over 7 grains per gallon of hardness is considered significantly hard.
What Do the "Sizes" on Water Softeners Mean?
Water softener sizes are usually given as the number of grains of hardness the softener can treat before its treatment bed needs regeneration.
For example, a 32,000 grain softener has the capacity to exchange 32,000 grains of hardness before regeneration is required.
The higher the hardness level of the water, the fewer gallons of water the softener will treat between regenerations. To determine the gallons that can be treated, divide the hardness level of the water, its grains per gallon number, into the total capacity of the water softener.
If your water has 8 grains of hardness, the 32,000 grain softener will treat 4,000 gallons of water between regenerations (32,000 divided by 8); if your water has 25 grains of hardness, the 32,000 grain softener will treat only 1,280 gallons of water between regenerations (32,000 divided by 25).
Most residential softeners fall in the range of 15,000 to 64,000 grains in capacity. Around 24,000 or 32,000 grains is an average sized softener.
Brine and Resin: How Do Softeners Regenerate Themselves?
Water softeners have the ability to renew their hardness reduction capacity to almost their original stated capacity rating. They do this by rinsing their treatment medium, called resin, with a strong salt water solution, called brine.
The softener consists of two separate tanks. The first, usually a tall, thin tank called a mineral tank, is about 2/3 full of specially made beads called resin. When the resin is new, it is charged with a strong load of sodium ions.
The second tank, called a brine tank, is shorter. It is filled with salt and has a few gallons of water in the bottom.
As water passes through the resin bed on the way toyour home, sodium is exchanged for calcium and magnesium, and the softener’s resin becomes loaded with calcium and magnesium and depleted of sodium. The softener must then regenerate itself by drawing a strong solution of brine, very salty water, from the bottom of the brine tank and passing it through the resin bed. The brine solution is so strong that it displaces the calcium and magnesium from the resin and they are washed down the drain. The sodium from the brine solution is left on the resin and the softener is again ready to treat hard water.
As part of the regeneration process, the softener also "backwashes" the resin bed by running water through it from the bottom to the top, to clean out the bed and resettle it. It also gives the bed a good downward rinse.
Control Valve Types. How does the Softener Knows When to Regenerate Its Resin?
The water softening process is overseen by a control valve that sits on top of the mineral tank. Although marketers apply clever names to these control devices, they really fall into two distinct classes: timers and meters.
Timers, the older style, are also called “day clocks.” They work like a standard electric timing device. The user sets the days of regeneration—every fourth day, for example--and the timer regenerates the softener in the early morning hours of every fourth day.
Meters, on the other hand, are given basic information—like the hardness of the water and the number of users, or the pre-calculated capacity in gallons. The metered control valve then actually counts the number of gallons of water used and regenerates when the resin bed is near exhaustion.
Timer Vs. Meter. Which Is Better?
Neither is better. They’re just different. It is fashionable now to present meter-controlled softeners as “green” products. The truth is that a poorly programmed meter system can be as wasteful as a poorly programmed timer model. For most standard installations, the meter is a better option, but only if it is programmed correctly. For many situations—where the softener is used to reduce iron in well water, for example—a timer valve is usually more practical.
Either a timer or meter can be programmed mechanically or electronically.
Programming Options. Electro-Mechanical or Full-Electronic SXT?
The softener can be given information with either an essentially mechanical or an electronic control system. If you're comfortable with programming clocks or VCRs electronically, you'll probably like the full electronic softener best. With some control valves, the full electronic SXT version allows you to fine tune the softener's performance more accurately. The electro-mechanical control, however, is very easy to use, and it works fine. With most controls, programming is quicker with the electro-mechanical version.
What is Resin? Is Fine Mesh or Standard Best?
Modern softeners use a man-made plastic bead known as “strong acid cation” resin. Resin is made of divinylbenzene (DVB) and consist of spherical beads ranging from 0.3 millimeter to 1.2 millimeter in diameter (16 to 50 mesh). There is also a “fine mesh” variety that is smaller in diameter, in the 50 to 70 mesh range.
Most residential softeners have standard resin. Fine mesh is most often used for removing iron from well water, but it also has excellent softening properties.
The main disadvantage of fine mesh is that it restricts service flow more than standard mesh. Fine mesh resin uses less water and less salt and has a bit faster exchange rate as compared with standard resin, but in our opinion, unless you are removing iron from well water, standard resin is a better choice for most residential users.
How do you pick the correct size softener?
This can be very complicted or very simple. One rule is that oversizing is often wasteful. This is an area where the bigger the better rule doesn't apply.
Here is the simple version.
A very simple way to get a good "ballpark" size for a resiential softener is to use this formula:
Hardness of the water in grains times the number of people who use the water times 75 times 7= softener size in grains per gallon. (The 7 is for the days in a week and the 75 is a guess at how many gallons per day each person will use.)
For example. You have a family of 4 and a hardness level of 12 grains per gallon.
12 X 4 X 75 X 7 = 25,200.
Therefore, a 24,000 grain softener would work, but a 32,000 grain would be a excellent choice and would give you a bit of room to adjust for optimal salt setting. In spite of what the home-demo seller might say, a 64,000 grain unit is not a good idea.
As I said, this is the simple version, and there are other considerations. But in general terms, following the formula will give you the size of a softener that will provide soft water for your home for about a week between regenerations.
You can get as complicated as you want in softener sizing, but if you follow the formula above your softener will be sized better than the majority of the softeners sold in the US.
How about the complicated version?
If you want to fine tune the softener so it's as economical as possible in its salt and water consumption, a bit of oversizing is necessary. For example, the family of four described above can use less salt if they'll buy a 40,000 grain softener and run it at a reduced salt setting. This is explained and illustrated in some detail in our disucssion of how metered softener controls work. (Keep in mind that although you'll save salt with a reduced salt setting, you'll use more water.)