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Water hardness does not affect human health, but does affect the suitability use of water for different uses.
Water moving through soil and rock dissolves very small amounts of minerals, then holds them in solution. The two most common minerals that make water “hard” are calcium and magnesium. “Hardness” increases as the dissolved calcium and magnesium content increases.
Other ions that produce hardness include iron, manganese, strontium, barium, zinc and aluminum but, as a rule, these are not present in significant quantities.
Hard water is not a health hazard. It can contribute toward dietary requirements for calcium and magnesium. Research suggests a correlation between hard water and lower cardiovascular disease mortality.
The ion exchange process to soften water exchanges sodium for calcium and magnesium. This typically adds about 8 mg/L sodium for each grain per gallon of hardness removed. Each 1 mg/L sodium in drinking water is equivalent to 1.1 milligram of sodium for each quart of water consumed.
Individuals on a restricted sodium diet may be advised by their physician:
Hard water impacts nearly all household cleaning tasks, including dish washing, laundry, and bathing. The amount of soap and detergent required to clean effectively is affected by the dissolved mineral content – the degree of hardness.
Soap combines with hard water minerals to form a sticky soap “curd”. This curd can leave a sticky film on skin, also making hair dull, lifeless and difficult to manage.
Soap curd can lodge in fabric during laundry in hard water, making fabric stiff and rough. Soil and stains are not completely removed during washing so white fabrics turn gray and colors lose brightness. A sour odor can develop in clothes. Over time, laundering in hard water may reduce the life of clothes.
Some synthetic detergents are less effective in hard water because the active ingredient is partially inactivated by hardness.
Soap curd can leave deposits on dishes, sinks, bathtubs, showers, and plumbing fixtures.
Water-using appliances tend to lose efficiency and fail more frequently as water hardness increases. Calcium and magnesium minerals form scale deposits when hard water is heated. Pipes and plumbing fixtures can become clogged with scale that reduces water flow and ultimately requires replacement.
Softened water is also not recommended for watering plants, lawns, and gardens due to its sodium content. Sodium accumulations can cause soil structure to deteriorate resulting in crusting and loss of water infiltration.
Water hardness is typically expressed as “grains of hardness per gallon of water (grains/gal)” or “milligrams of hardness per liter of water (mg/L)”. Hardness is further expressed as a calcium carbonate (CaCO3) equivalent. Classifications of water hardness expressed as calcium carbonate follow:
Water softening units can be installed into household plumbing systems to continuously remove calcium and magnesium. There are a number of water treatment methods with corresponding differences in costs and effectiveness. The ion exchange resin method is most commonly used
¶ Table 1. Water Hardness Classification (as CaCO3) |
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| Category | Hardness as mg/l | Hardness as grains/gallon |
| Soft | < 17 | < 1.0 |
| Slightly hard | 17 - 60 | 1.0 - 3.5 |
| Moderately hard | 60 - 120 | 3.5 - 7.0 |
| Hard | 120 - 180 | 7.0 - 10.5 |
| Very hard | 180 - 270 | 10.5 - 16.0 |
| Extremely hard | 270 - 400 | 16.0 - 23.5 |
| Brackish | > 400 | > 23.5 |
Water is "softened" by removing calcium and magnesium and replacing with sodium. Softening water to remove hardness has no direct effect on drinking water safety, but may improve the performance of appliances. Softening improves detergent performance and helps eliminate lime deposits. Softened water may not be desirable for watering plants, lawns, and gardens if the sodium content is excessive. The right combination of water pH and alkalinity may render certain waters to be corrosive, so equipment adjustments may be necessary. Corrosive waters have potential to leach heavy metals from pipes, solder, and plumbing fixtures of older systems. Testing for lead and copper may be prudent if waters are determined to be corrosive.
Water hardness results from dissolved calcium and magnesium minerals. Water is "softened" by removing the calcium and magnesium and replacing with sodium. Softening has no direct effect on drinking water safety. Softening helps eliminate lime deposits and improves detergent performance.
Water hardness results from dissolved calcium and magnesium minerals. Hardness has no direct effect on drinking water safety, but affects performances. Hard water requires more detergent for cleaning and may form "soap scum". When heated above 140°F, hardness minerals may form scale deposits in plumbing and appliances. If water is heated, frozen, minerals may precipitate and form deposits in ice and beverages. Pretreatment with a water softener, softening agent to remove calcium and magnesium may be beneficial.
Water hardness results from dissolved calcium and magnesium minerals. Hardness has no direct effect on drinking water safety, but hard water requires more detergent for cleaning and may form "soap scum". Hardness minerals may form scale deposits in plumbing and appliances when heated above 140°F. Minerals may precipitate and form deposits in ice and beverages, if water is heated, frozen, . Pretreatment with a water softener, softening agent to remove calcium and magnesium may be beneficial.
Water hardness results from dissolved calcium and magnesium minerals. Heating this water will likely result in scale deposits forming in appliances, plumbing, and fixtures. Heating, freezing water may cause the hardness minerals (calcium and magnesium) to precipitate and form deposits in beverages and ice. Hardness has no direct effect on drinking water safety, but very hard water can have a chalky, bitter,, mineral aftertaste for some individuals. Pretreatment with a water softener, softening agent to remove calcium and magnesium may be beneficial.
Water hardness results from dissolved calcium and magnesium minerals. Hardness has no direct effect on drinking water safety, but this water may have a chalky, bitter,, mineral aftertaste. Scale deposits are likely to form in appliances, plumbing, beverages, and ice, especially when water is heated, frozen. Use of this water supply without treatment may shorten the life of plumbing, fixtures, and appliances (like water heaters) due to scale formation. Pretreatment with a water softener, softening agent to remove calcium and magnesium may be needed for specific uses.
Water hardness results from dissolved calcium and magnesium minerals. Hardness itself does not pose a health risk, but this water is likely to have a chalky, bitter, or mineral aftertaste. Heavy scale and mineral buildup on plumbing fixtures and appliances is expected. Corrosion of certain metals may occur, depending on other water characteristics. Using this water supply for watering plants may lead to salt and mineral buildup in the soil. Intensive pretreatment by water softening or using softening agents may be necessary for specific uses.
USDA Extension. 2019. Drinking Water Contaminant – Hard water. accessed 06July2022. https://drinking-water.extension.org/drinking-water-contaminant-hard-water/
Bradshaw & Powell. 2000. Bull. MF-912. Understanding Your Water Test Report. Kansas State Univ. Coop. Ext. Svc., Manhattan KS 12 pg.