- What impurities will softeners remove
- How is hardness measured?
- Problems caused by hard water
- The ion exchange process
- Water testing
- Health risks associated with softened water
- Types of water softening equipment available
- Operation and maintenance
- Cost of water softeners and supplies
- Advantages/Disadvantages of water softeners
- Alternatives to ion exchange units
- Magnetic conditioning
- Items to consider when purchasing an ion exchange water softener
- Further information
What impurities will softeners remove?
Water softeners will remove nearly all the calcium and magnesium from the raw water during the softening process. Softeners will also remove up to 10 ppm of iron and manganese. Water supplies with high levels of iron and manganese (greater than 10 ppm) may need pretreatment to prolong the lifespan of a water softener.
What makes water “hard”?
Groundwater dissolves rocks and minerals releasing calcium and magnesium ions that cause water to be hard. These dissolved ions give hard water its characteristics.
How is hardness measured?
Water hardness ordinarily is expressed in grains of hardness per gallon (gpg) of water. Water impurities can also be measured in either parts per million (ppm) or milligrams per liter (mg/l). One gpg is equal to 17 ppm (mg/l). Table 1 shows how hardness is classified.
Table 1. Hardness Classification
hardness minerals milligrams per
in grains per liter (mg/l) or
gallon (gpg) Level of Hardness parts per million (ppm)
below 1.0 soft less than 17
1.0 to 3.5 slightly hard 17 to 60
3.5 to 7.0 moderately hard 61 to 120
7.0 to 10.5 hard 121 to 180
above 10.5 very hard more than 180
Problems Caused by Hard Water
Hard water interferes with all types of cleaning tasks. Cleaning problems arise when the cleaning agents do not fully remove dirt and grime. Over time, clothes washed in hard water may look dingy and feel harsh and scratchy. White clothing continually washed in hard water will gradually show a grayish tinge. Dishes and glassware washed in dishwashers using hard water may be spotted when dry. Hard water causes films on glass shower doors, walls and bathtubs. Hair washed in hard water may feel sticky and look dull.
Regular soaps combine with dissolved calcium and magnesium to form soap curds or soap scum. Soap scum is difficult to remove from sinks and appliances.
Household appliance performance may be affected by hard water use. When heated, calcium carbonate and magnesium carbonate are removed from the water and produce a scale buildup in the hot water heater. A large scale buildup slows the heating process and requires more energy to heat water. Water heaters with large accumulations of mineral buildup will have shorter life spans. Scale deposits also corrode and plug plumbing fixtures and accumulate in other appliances affecting their performance.
The Ion Exchange Process
Calcium (Ca2+) and magnesium (Mg2+) ions that cause water hardness can be removed fairly easily by using an ion exchange procedure. Water softeners are cation exchange devices. Cations refer to positively charged ions. Cation exchange involves the replacement of the hardness ions with a nonhardness ion. Water softeners usually use sodium (Na+) as the exchange ion. Sodium ions are supplied from dissolved sodium chloride salt, also called brine. In the ion exchange process, sodium ions are used to coat an exchange medium in the softener. The exchange medium can be natural “zeolites” or synthetic resin beads that resemble wet sand.
As hard water passes through a softener, the calcium and magnesium trade places with sodium ions (Figure 1). Sodium ions are held loosely and are easily replaced by calcium and magnesium ions. During this process free sodium ions are released to the water.
NaZeolite + Ca2 –> CaZeolite + Na+
NaZeolite + Mg2+ –> MgZeolite + Na+
After softening a large quantity of hard water the exchange medium becomes coated with calcium and magnesium ions. When this occurs, the exchange medium must be recharged or regenerated (Figure 1). To recharge the softener with sodium ions, a softener is backflushed with a salt brine solution. During a backflush the brine solution replaces the calcium and magnesium ions on the exchange medium with sodium ions from the salt solution.
NaC1 + CaZeolite –> NaZeolite + CaC1
NaC1 + MgZeolite –> NaZeolite + MgC1
The time between recharging cycles depends on the hardness of the water, the amount of water used, the size of the unit, and the capacity of the exchange media to remove hardness.
Before buying any water treatment equipment, you should know what impurities are found in the water supply. Types and amounts of impurities in your water can be determined by a certified laboratory. The results of the water test will help determine if softening is needed. The water testing may reveal if other water treatment is required.
If you obtain water from a private water supply, water testing is your responsibility. Water testing should be done on a regular basis. If a problem is suspected, test more often.
Community water supplies are monitored and treated to protect users from health threatening water impurities. Ask your supplier for a copy of the latest water test results.
Hard water is considered a nuisance water problem. Hardness removal is not a necessity to protect your health. Water softening is popular because most people prefer softened.
Health Risks Associated with Softened Water
During the softening process sodium is released from the exchange media into the output water. For every grain of hardness removed from water, 8 mg/1 (ppm) of sodium is added. People on restricted sodium intake diets should account for increased levels of sodium in softened water. Your family physician should be consulted. Sodium intake from softened water can be avoided by leaving one kitchen tap unsoftened for drinking and cooking.
Types of Water Softening Equipment available
Water softeners are classified in five different categories:
1. Manual: There are several types of manual softeners. The operator opens and closes valves to control the frequency, rate and time length of backflushing or recharging.
2. Semi-automatic: The operator initiates only the recharging cycle. A button is pushed when the softener needs recharging and the unit will control and complete the recharging process.
3. Automatic: The automatic softener usually is equipped with a timer that automatically initiates the recharging cycle and every step in the process. The operator needs only to set the timer and add salt when needed. It is the most popular type of softener used.
4. Demand initiated regeneration (DIR): All operations are initiated and performed automatically in response to the water use demand for softened water. DIR systems generally have two softening tanks and a brine tank. While one tank is softening the other tank is recharging.
5. Off-site regeneration (generally rental units): A used softening tank is physically replaced with a recharged tank. Spent softening tanks are then recharged at a central location.
Operation and maintenance
Maintenance of water softeners is largely confined to restocking the salt supply for the brine solution. With manual and semiautomatic models, the owner will also have to start the recharging cycle. Salt can be purchased in the form of pellets, granules or blocks.
The brine tank may require periodic cleaning. The frequency of cleaning depends on the amount and purity of the salt used in the softening process. The brine valve and float assembly should also be checked and cleaned as often as needed.
The presence of excess iron or hydrogen sulfide can inhibit the effectiveness of a water softening unit. Installation of the proper presoftening treatment equipment may be required (see the Iron and Manganese circular in the Household Water Treatment series). Water test results will help make that determination. More frequent back-washing or reversing the normal flow of water through the treatment unit may be required to remove iron buildup.
Cost of Water Softeners and supplies
Retail prices for home water softeners may range from approximately Rs.60,000 to Rs.1200,000 or more depending on the size and type of softener. Softeners are rated by the total number of grains the unit can remove before being recharged. Cost of salt is approximately Rs.50 to Rs. 1000/ per regenerate depending on the form purchased.
Russell Derickson, Extension Associate in Water and Natural Resources, South Dakota Extension Service
Bruce Seelig, Water Quality Specialist, North Dakota Extension Service
Fred Bergsrud, Water Quality Coordinator, Minnesota Extension Service