In today’s busy world, little thought is given to something as basic as the operation of the water softener that is serving useful duty somewhere around the water heater, usually in the basement. The average consumer, when asked how a water softener works, will usually admit that they do not know and, generally, do not care as long as it works. When asked what type of salt they use in their softener, the response is usually "which ever is most easily available or least expensive." The factors involved in selecting a salt, although not complex, are very important to efficient operation of a water softener. Many items affect the efficiencies of a water softener; among the most noticeable are the softener’s economy, long-term performance and health and environmental impact. In the new millennium, there are more salts available to the consumer than in any time in the past. A good starting point is to review a water softener’s operation and the salt options available to the consumer.
Hard water is found worldwide and in approximately 85 percent of the United States, according to the U.S. Geological Survey. Hard water areas exist where water has access to rock that contains calcium, magnesium or a combination of both. The U.S. Department of the Interior has established levels for the class of water. (See Table 1.)
The harder the water, the more it affects the operation of the household. The effect is most noticeable in the laundry and bath. (It should be noted that even moderately hard water makes a difference.)
A water softener works on the principal of ion exchange. This is a process where positive electrically charged atoms of hardness minerals in water such as calcium and magnesium are exchanged for sodium or potassium ions supplied by the salt. The exchange occurs when water passes over the surface of divinylbenzene resin beads in the water softener. As the water passes over the surface, the resin bead substitutes sodium or potassium for the calcium or magnesium attached to the bicarbonate in the hard water. Sodium or potassium bicarbonates do not contribute to the hardness of the water, hence the water is considered soft.
Compacted potassium chloride began as a healthy alternative to salt and in the past ten years has become a viable water product based on its own merits. A significant benefit to potassium chloride is the impact on sodium in drinking water. Studies have found that not only does water softened with potassium chloride not add sodium to drinking water but will remove up to 90 percent of the existing sodium in softened water.1
A second benefit of potassium chloride is its environmental impact. California is looking at the amount of sodium chloride that is being discharged to the drain and then regulating softener use. In areas where sodium discharge is an issue, the quickest remedy is to convert to potassium chloride. Potassium chloride is generally very pure, often more than 99 percent potassium chloride. The color can range from light pink to white but is generally white in color and is a compacted cube in texture.
Compacted evaporated salt is the purest and cleanest salt that can be used in a water softener. This product generally is made of salt compacted from evaporated salt of 99.8 percent purity or higher. The evaporation process assures that the salt is cleaner and purer than salt from any other salt production process. The cleaner product is important when considering long-term operation of the water softener. It is well-known that as a water softener ages, salt quality can dramatically affect the efficiency and performance of the water softener.
The two common forms of compacted evaporated salt are pellets and cubes. The pellets are oval shaped and the cubes are random sized pieces from a compacted sheet of salt. Each can contain iro-removal agents and resin-cleaning agents to prolong water softener life. Unlike rock or solar salt, evaporated salt contributes fewer impurities.
Extra coarse solar salt is produced as the result of solar evaporation of ponds containing weak brine solutions from either ocean or large saline lakes such as the Great Salt Lake in the United States. Over time, the water is evaporated from the brine, and salt crystallizes from the solution. Depending on the environmental conditions, the crystals vary in size from large to very small. The very small particles usually are returned to the brine source, and the large crystals are broken into smaller material. A portion of solar salt that has been determined to be the most efficient crystal size for the average water softener is screened from the salt. The portion is bagged as solar extra coarse water conditioning salt and is readily available in the western and northern United States. Solar salt is a pure salt, often achieving purities of evaporated salts, but is produced by open evaporation and will have residue from this process either in or on the salt crystals. Dirt or organic matter from the solar pond where the salt was harvested may be included within the salt crystal or on the crystal surface. The purity of solar salt is usually above 99.0 percent, and the color is usually white or off-white.
Compacted solar salt is a product found primarily in the western United States, where the availability of evaporated compacted salt is less common. The compacted products are available in both pellets and cubes and with iron removal additives. The pieces of compacted solar salt are larger than solar extra coarse and tend to perform more efficiently in a water softener than solar extra coarse. The purity and impurities in the product are very similar to that of solar extra coarse salt.
Rock salt is one of the earliest types of salt supplied for water softeners. It has the advantage of being less expensive and readily available. Rock salt is produced in a particle size that works well in a water softener but has no refining after it is removed from the salt strata underground. The result of the lack of refining is a product that has high levels of insoluble material. The insoluble material will deposit in the salt storage tank on the water softener, which will require more frequent cleaning of the water softener. Although the amount of insoluble material varies, it can be as high as 5 percent in some regions. Generally, there is between 1 and 2 percent insoluble material in most water-conditioning rock salt on the market. With 2 percent insolubles in the salt, the average family of four with a timer type water softener could find as much as 20 pounds of insoluble matter in its softener per year. Rock salt is approximately 98.5 percent sodium chloride and 1.5 percent insoluble material. The color of the salt is white with either black or white insoluble matter. (Black insoluble matter is typical of rock salt from the northern United States and white insoluble matter is common in salt from the southern United States.)
Optically sorted rock salt has been available in selected markets for the last 10 to 15 years. This product is available in the northern United States and actually has the dark impurities removed from the rock salt during processing by an optical sorter. The process cleans the salt by removing dark-colored insoluble material and raises the purity of the product about 1 percent. This process will remove more than half and as high as 80 percent of the insoluble material in the rock salt. The results of optically sorting are very dramatic and can reduce the insoluble levels in the rock salt to parity with solar salt. Average purity of optically sorted rock salt is 99.5 percent with a much whiter appearance than normal rock salt.
As more homeowners become aware of the advantages of water softeners, salt use will increase. Currently, communities are focusing on the issue of salt discharged to the sewer systems and discharged into lateral fields attached to septic tanks. There has been a significant amount of work done that shows salt does not damage septic tanks or lateral fields. But in the past few years, there has been concern expressed by the Canadian legislature to the possible breakdown of certain soil types from salt espouse.
In the past few years, a ban of water softeners in several areas of California was fought by the Water Quality Association and, in most cases, was reversed. In Connecticut, the state legislature is in the process of introducing regulations that will prohibit the use of sodium chloride in water softeners that discharge to septic systems or dry wells.
The state of California has recently enacted legislation SB1006 that requires significant improvement in the performance of water softeners in the state by 2002. The efficiency requirements for water softeners will virtually eliminate the use of timer-type water softeners. The direction of the bill is to encourage improvements in regeneration and softener efficiencies. The timer softener, although known as the "workhorse" of the industry, is inefficient and notorious for overusing salt. The efficiencies listed in the legislation are actually too rigorous for potassium chloride water softening and require almost ideal performance from sodium chloride. This is an issue that the industry is currently analyzing to determine the best solution.
The use of water softener regenerants requires a balance of the properties most important to the consumer. The use of salt is under more scrutiny by environmental agencies, but using efficient water softeners and resins can easily control concerns. The next few years will require adjustment in consumers’ attitudes toward the type of softener used and which salt is placed in the softener. The economics and advantages of soft water, especially in extreme hard water areas, dictate that these decisions will benefit all consumers in the long-term.
About the Author
Jerry Poe is technical director for IMC Salt Co. He oversees technical effort for three plants in Canada, three in the United States, one in England and one mine in each of these countries. In addition, he oversees market and sales support and new product development.
Grains Per Gallon Hardness
< 1 Soft
1 – 3.5 Slightly Hard
3.5 – 7.0 Moderately Hard
7.0 – 10.5 Hard
> 10.5 Very Hard
In response to concerns over salt discharge in sewer systems and lateral fields attached to septic tanks, the research and development department of IMC Salt performed a study in Strasbourg, Saskatchewan, to determine the impact on the quality of the waste effluent from their sewage lagoon.
The test involved converting the town from sodium chloride to potassium chloride to study the impact on the quality of the waste effluent from its lagoon, which is used to irrigate agricultural land.
The population of the city was 800 residents at the time of the test, with 430 water meters and a water hardness of 26 grains per gallon. Significant improvements were made in the irrigation water quality by reducing the sodium absorption ratio (SAR) from 6.8 to 2.8. (SAR is a measure of the rate at which sodium percolates through the soil and its impact on the soil.)
It was noted from the test that sodium chloride as a water softener salt was responsible for more than 50 percent of the sodium in the waste effluent.