Hard Water
From Wikipedia, the free encyclopedia
Hard water is water that has high mineral content (mainly calcium and magnesium ions) (in contrast with soft water). Hard water minerals primarily consist of calcium (Ca2+), and magnesium (Mg2+) metal cations, and sometimes other dissolved compounds such as bicarbonates and sulfates. Calcium usually enters the water as either calcium carbonate (CaCO3), in the form of limestone and chalk, or calcium sulfate (CaSO4), in the form of other mineral deposits. The predominant source of magnesium is dolomite (CaMg(CO3)2). Hard water is generally not harmful to one's health.
The simplest way to determine the hardness of water is the lather/froth test: soap or toothpaste, when agitated, lathers easily in soft water but not in hard water. More exact measurements of hardness can be obtained through a wet titration. The total water 'hardness' (including both Ca2+ and Mg2+ ions) is read as parts per million (ppm) or weight/volume (mg/L) of calcium carbonate (CaCO3) in the water. Although water hardness usually only measures the total concentrations of calcium and magnesium (the two most prevalent, divalent metal ions), iron, aluminium, and manganese may also be present at elevated levels in some geographical locations.
Water Softening
From Wikipedia, the free encyclopedia
A water softener reduces the dissolved calcium, magnesium, and to some degree manganese and ferrous iron ion concentration in hard water. A common water softener is sodium carbonate; formula Na2CO3.
These "hardness ions" cause three major kinds of undesired effects. Most visibly, metal ions react with soaps and calcium-sensitive detergents, hindering their ability to lather and forming a precipitate—the familiar "bathtub ring". Presence of "hardness ions" also inhibits the cleaning effect of detergent formulations.
Second, calcium and magnesium carbonates tend to precipitate out as hard deposits to the surfaces of pipes and heat exchanger surfaces. This is principally caused by thermal decomposition of bi-carbonate ions but also happens to some extent even in the absence of such ions. The resulting build-up of scale can restrict water flow in pipes. In boilers, the deposits act as an insulation that impairs the flow of heat into water, reducing the heating efficiency and allowing the metal boiler components to overheat. In a pressurized system, this can lead to failure of the boiler.[1]
Third, the presence of ions in an electrolyte, in this case, hard water, can also lead to galvanic corrosion, in which one metal will preferentially corrode when in contact with another type of metal, when both are in contact with an electrolyte. However the sodium (or potassium) ions released during conventional water softening are much more electrolytically active than the calcium or magnesium ions that they replace and galvanic corrosion would be expected to be substantially increased by water softening and not decreased[citation needed]. Similarly if any lead plumbing is in use, softened water is likely to be substantially more plumbo-solvent than hard water[citation needed].
Contents
Conventional water-softening devices intended for household use depend on an ion-exchange resin in which "hardness" ions trade places with sodium ions that are electrostatically bound to the anionic functional groups of the polymeric resin. A class of minerals called zeolites also exhibits ion-exchange properties; these minerals were widely used in earlier water softeners. Water softeners may be desirable when the source of water is a well, whether municipal or private.
How it works
The water to be treated passes through a bed of the resin. Negatively-charged resins absorb and bind metal ions, which are positively charged. The resins initially contain univalent hydrogen, sodium or potassium ions, which exchange with divalent calcium and magnesium ions in the water. As the water passes through the resin column, the hardness ions replace the hydrogen, sodium or potassium ions which are released into the water. The "harder" the water, the more hydrogen, sodium or potassium ions are released from the resin and into the water.
Resins are also available to remove carbonate, bi-carbonate and sulphate ions which are absorbed and hydroxyl ions released from the resin. Both types of resin may be provided in a single water softener.
Regeneration
As these resins become loaded with undesirable cations and anions they gradually lose their effectiveness and must be regenerated. If a cationic resin is used (to remove calcium and magnesium ions) then regeneration is usually effected by passing a concentrated brine, usually of sodium chloride or potassium chloride, or hydrochloric acid solution through them.
For anionic resins a solution of sodium or potassium hydroxide (lye) is used. Most of the salts used for regeneration gets flushed out of the system and may be released into the soil or sewer. These processes can be damaging to the environment, especially in arid regions.[citation needed] Some jurisdictions prohibit such release and require users to dispose of the spent brine at an approved site or to use a commercial service company. Most water softener manufacturers provide metered control valves to minimize the frequency of regeneration. It is also possible on most units to adjust the amount of reagent used for each regeneration. Both of these steps are recommended to minimize the impact of water softeners on the environment and conserve on reagent use. Using acid to regenerate lowers the pH of the regeneration waste.
If potassium chloride is used the same exchange process takes place except that potassium is exchanged for the calcium, magnesium and iron instead of sodium. This is a more expensive option and may be unsuited for people on potassium-restricted diets.
Effects of sodium
For people on a low-sodium diet, the increase in sodium levels (for systems releasing sodium) in the water can be significant, especially when treating very hard water. A paper by Kansas State University gives an example: "A person who drinks two litres (2L) of softened, extremely hard water (assume 30 gpg) will consume about 480 mg more sodium (2L x 30 gpg x 8 mg/L/gpg = 480 mg), than if unsoftened water is consumed." This is a significant amount, as they state: "The American Heart Association (AHA) suggests that the 3 percent of the population who must follow a severe, salt-restricted diet should not consume more than 400 mg of sodium a day. AHA suggests that no more than 10 percent of this sodium intake should come from water. The EPA’s draft guideline of 20 mg/L for water protects people who are most susceptible." Most people who are concerned with the added sodium in the water generally have one tap in the house that bypasses the softener, or have a reverse osmosis unit installed for the drinking water and cooking water, which was designed for desalinisation of sea water.
A Bit too Scientific
If you have made it this far you might be saying a lot of this was over my head. There is a lot of science in water quality. For most you will know you have hard water by the calcium deposits on your plumbing fixtures. It can build up in your pipes and reduce the water flow and can eventually damage valves and other plumbing parts. In the column to the right is informaiton related to the water used here in Johnson county. Our water at the tap is not overly hard but hard enough to cause plumbing problems. Adding a water softener can make your water feel much better if you like the smooth, clean, and slick feeling. If you don't like that slick feeling than there are ways to partially soften the water in your house that will help your appliences without making yoru shower too slick. As for salt consumption I have a pretty standard softener with on demand regeneration in my house. We have four of us in the house I use about three 40# bags of salt a year which costs around $5 each. So after the initial instalaltion the ongoing expense is not too great. If you are interested in what a softener can do for you please give me a call. 913-593-5074