Soft drinks are enormously popular beverages consisting primarily of carbonated water, sugar, and flavorings. Nearly 200 nations enjoy the sweet, sparkling soda with an annual consumption of more than 34 billion gallons. Soft drinks rank as America's favorite beverage segment, representing 25% of the total beverage market. In the early 1990s per capita consumption of soft drinks in the U.S. was 49 gallons, 15 gallons more than the next most popular beverage, water.
The roots of soft drinks extend to ancient times. Two thousand years ago Greeks and Romans recognized the medicinal value of mineral water and bathed in it for relaxation, a practice that continues to the present. In the late 1700s Europeans and Americans began drinking the sparkling mineral water for its reputed therapeutic benefits. The first imitation mineral water in the U.S. was patented in 1809. It was called "soda water" and consisted of water and sodium bicarbonate mixed with acid to add effervescence. Pharmacists in America and Europe experimented with myriad ingredients in the hope of finding new remedies for various ailments. Already the flavored soda waters were hailed as brain tonics for curing headaches, hangovers, and nervous afflictions.
Pharmacies equipped with "soda fountains" featuring the medicinal soda water soon developed into regular meeting places for local populations. Flavored soda water gained popularity not only for medicinal benefits but for the refreshing taste as well. The market expanded in the 1830s when soda water was first sold in glass bottles. Filling and capping the gaseous liquid in containers was a difficult process until 1850, when a manual filling and corking machine was successfully designed. The term "soda pop" originated in the 1860s from the popping sound of escaping gas as a soda bottle was opened.
New soda flavors constantly appeared on the market. Some of the more popular flavors were ginger ale, sarsaparilla, root beer, lemon, and other fruit flavors. In the early 1880s pharmacists experimented with powerful stimulants to add to soda water, including cola nuts and coca leaves. They were inspired by Bolivian Indian workers who chewed coca leaves to ward off fatigue and by West African workers who chewed cola nuts as a stimulant. In 1886 an Atlanta pharmacist, John Pemberton, took the fateful step of combining coca with cola, thus creating what would become the world's most famous drink, "Coca-Cola". The beverage was advertised as refreshing as well as therapeutic: "French Wine Cola—Ideal Nerve and Tonic Stimulant." A few years later another pharmacist, Caleb Bradham, created "Pepsi-Cola" in North Carolina. Although the name was a derivation of pepsin, an acid that aids digestion, Pepsi did not advertise the beverage as having therapeutic benefits. By the early 20th century, most cola companies focused their advertising on the refreshing aspects of their drinks.
As flavored carbonated beverages gained popularity, manufacturers struggled to find an appropriate name for the drinks. Some suggested "marble water," "syrup water," and "aerated water." The most appealing name, however, was "soft drink," adapted in the hopes that soft drinks would ultimately supplant the "hard liquor" market. Although the idea never stuck, the term soft drink did.
Until the 1890s soft drinks were produced manually, from blowing bottles individually to filling and packaging. During the following two decades automated machinery greatly increased the productivity of soft drink plants. Probably the most important development in bottling technology occurred with the invention of the "crown cap" in 1892, which successfully contained the carbon dioxide gas in glass bottles. The crown cap design endured for 70 years.
The advent of motor vehicles spawned further growth in the soft drink industry. Vending machines, serving soft drinks in cups, became regular fixtures at service stations across the country. In the late 1950s aluminum beverage cans were introduced, equipped with convenient pull-ring tabs and later with stay-on tabs. Light-weight and break-resistant plastic bottles came into use in the 1970s, though it was not until 1991 that the soft drink industry used plastic PET (polyethylene terephthalate) on a wide scale.
Soft drink manufacturers have been quick to respond to consumer preferences. In 1962 diet colas were introduced in response to the fashion of thinness for women. In the 1980s the growing health consciousness of the country led to the creation of caffeine-free and low-sodium soft drinks. The 1990s ushered in clear colas that were colorless, caffeine-free, and preservative-free.

Raw Materials

Carbonated water constitutes up to 94% of a soft drink. Carbon dioxide adds that special sparkle and bite to the beverage and also acts as a mild preservative. Carbon dioxide is an uniquely suitable gas for soft drinks because it is inert, non-toxic, and relatively inexpensive and easy to liquefy.
The second main ingredient is sugar, which makes up 7-12% of a soft drink. Used in either dry or liquid form, sugar adds sweetness and body to the beverage, enhancing the "mouth-feel," an important component for consumer enjoyment of a soft drink. Sugar also balances flavors and acids.
Sugar-free soft drinks stemmed from a sugar scarcity during World War II. Soft drink manufacturers turned to high-intensity sweeteners, mainly saccharin, which was phased out in the 1970s when it was declared a potential carcinogen. Other sugar substitutes were introduced more successfully, notably aspartame, or Nutra-Sweet, which was widely used throughout the 1980s and 1990s for diet soft drinks. Because some high-intensity sweeteners do not provide the desired mouth-feel and aftertaste of sugar, they often are combined with sugar and other sweeteners and flavors to improve the beverage.
The overall flavor of a soft drink depends on an intricate balance of sweetness, tartness, and acidity (pH). Acids add a sharpness to the background taste and enhance the thirst-quenching experience by stimulating saliva flow. The most common acid in soft drinks is citric acid, which has a lemony flavor. Acids also reduce pH levels, mildly preserving the beverage.
Very small quantities of other additives enhance taste, mouth-feel, aroma, and appearance of the beverage. There is an endless range of flavorings; they may be natural, natural identical (chemically synthesized imitations), or artificial (chemically unrelated to natural flavors). Emulsions are added to soft drinks primarily to enhance "eye appeal" by serving as clouding agents. Emulsions are mixtures of liquids that are generally incompatible. They consist of water-based elements, such as gums, pectins, and preservatives; and oil-based liquids, such as flavors, colors, and weighing agents. Saponins enhance the foamy head of certain soft drinks, like cream soda and ginger beer.
To impede the growth of microorganisms and prevent deterioration, preservatives are added to soft drinks. Anti-oxidants, such as BHA and ascorbic acid, maintain color and flavor. Beginning in the 1980s, soft drink manufacturers opted for natural additives in response to increasing health concerns of the public.
[pic]
Impurities in the water are removed through a process of coagulation, filtration, and chlorination. Coagulation involves mixing floc into the water to absorb suspended particles. The water is then poured through a sand filter to remove fine particles of Roc. To sterilize the water, small amounts of chlorine are added to the water and filtered out.

The Manufacturing
Process

Most soft drinks are made at local bottling and canning companies. Brand name franchise companies grant licenses to bottlers to mix the soft drinks in strict accordance to their secret formulas and their required manufacturing procedures.

Clarifying the water

• 1 The quality of water is crucial to the success of a soft drink. Impurities, such as suspended particles, organic matter, and bacteria, may degrade taste and color. They are generally removed through the traditional process of a series of coagulation, filtration, and chlorination. Coagulation involves mixing a gelatinous precipitate, or floc (ferric sulphate or aluminum sulphate), into the water. The floc absorbs suspended particles, making them larger and more easily trapped by filters. During the clarification process, alkalinity must be adjusted with an addition of lime to reach the desired pH level.

Filtering, sterilizing, and dechlorinating the water

• 2 The clarified water is poured through a sand filter to remove fine particles of floc. The water passes through a layer of sand and courser beds of gravel to capture the particles. • 3 Sterilization is necessary to destroy bacteria and organic compounds that might spoil the water's taste or color. The water is pumped into a storage tank and is dosed with a small amount of free chlorine. The chlorinated water remains in the storage [pic] tank for about two hours until the reaction is complete. • 4 Next, an activated carbon filter dechlorinates the water and removes residual organic matter, much like the sand filter. A vacuum pump de-aerates the water before it passes into a dosing station.

Mixing the ingredients

• 5 The dissolved sugar and flavor concentrates are pumped into the dosing station in a predetermined sequence according to their compatibility. The ingredients are conveyed into batch tanks where they are carefully mixed; too much agitation can cause unwanted aeration. The syrup may be sterilized while in the tanks, using ultraviolet radiation or flash pasteurization, which involves quickly heating and cooling the mixture. Fruit based syrups generally must be pasteurized. • 6 The water and syrup are carefully combined by sophisticated machines, called proportioners, which regulate the flow rates and ratios of the liquids. The vessels are pressurized with carbon dioxide to prevent aeration of the mixture.

Carbonating the beverage

• 7 Carbonation is generally added to the finished product, though it may be mixed into the water at an earlier stage. The temperature of the liquid must be carefully controlled since carbon dioxide solubility increases as the liquid temperature decreases. Many carbonators are equipped with their own cooling systems. The amount of carbon dioxide pressure used depends on the type of soft drink. For instance, fruit drinks require far less carbonation than mixer drinks, such as tonics, which are meant to be diluted with other liquids. The beverage is slightly over-pressured with carbon dioxide to facilitate the movement into storage tanks and ultimately to the filler machine.

Filling and packaging

• 8 The finished product is transferred into bottles or cans at extremely high flow rates. The containers are immediately sealed with pressure-resistant closures, either tinplate or steel crowns with corrugated edges, twist offs, or pull tabs. • 9 Because soft drinks are generally cooled during the manufacturing process, they must be brought to room temperature before labeling to prevent condensation from ruining the labels. This is usually achieved by spraying the containers with warm water and drying them. Labels are then affixed to bottles to provide information about the brand, ingredients, shelf life, and safe use of the product. Most labels are made of paper though some are made of a plastic film. Cans are generally pre-printed with product information before the filling stage. • 10 Finally, containers are packed into cartons or trays which are then shipped in larger pallets or crates to distributors.

Quality Control

Soft drink manufacturers adhere to strict water quality standards for allowable dissolved solids, alkalinity, chlorides, sulfates, iron, and aluminum. Not only is it in the interest of public health, but clean water also facilitates the production process and maintains consistency in flavor, color, and body. Microbiological and other testing occur regularly. The National Soft Drink Association and other agencies set standards for regulating the quality of sugar and other ingredients. If soft drinks are produced with low-quality sugar, particles in the beverage will spoil it, creating floc. To prevent such spoilage, sugar must be carefully handled in dry, sanitized environments.
It is crucial for soft drink manufacturers to inspect raw materials before they are mixed with other ingredients, because preservatives may not kill all bacteria. All tanks, pumps, and containers are thoroughly sterilized and continuously monitored. Cans, made of aluminum alloy or tin-coated low-carbon steel, are lacquered internally to seal the metal and prevent corrosion from contact with the beverage. Soft drink manufacturers also recommend specific storage conditions to retailers to insure that the beverages do not spoil. The shelf life of soft drinks is generally at least one year.

Recycling

The $27 billion dollar soft drink industry generated about 110 billion containers each year in the early 1990s. About half of soft drink containers were aluminum cans and the other half, about 35 billion, were PET plastic bottles. Nearly 60% of all soft drink containers were recycled, the highest rate for any packaging in the United States. Environmental concerns continued to lead to improvements and innovations in packaging technology, including the development of refillable and reusable containers.

The Future

In the 1990s there were more than 450 types of soft drinks on the market and new flavors and sweeteners are developed all the time to meet market demands. In the future, advanced technology will lead to greater efficiency of soft drink production at all stages. New methods of water clarification, sterilization, and pasteurization will improve production and minimize the need for preservatives in soft drinks. Concerns with consumer health, safety, and the environment will continue to have a positive impact on trends in the soft drink industry.
Hard water
Hard water is water that has high mineral content (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 measures only 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. Iron in this case is important for, if present, it will be in its tervalent form, causing the calcification to be brownish (the color of rust) instead of white (the color of most of the other compounds

Hardness

Hardness in water is defined as the presence of multivalent cations. Hardness in water can cause water to form scales and a resistance to soap. It can also be defined as water that does not produce lather with soap solutions, but produces white precipitate (scum). For example, sodium stearate reacts with calcium: 2C17H35COONa + Ca2+ → (C17H35COO)2Ca + 2Na+
Hardness of water may also be defined as the soap-consuming capacity of water, or the capacity of precipitation of soap as a characteristic property of water that prevents the lathering of soap.

Types of hard water

A distinction is made between 'temporary' and 'permanent' hard water.

Temporary hardness

Temporary hardness is caused by a combination of calcium ions and bicarbonate ions in the water. It can be removed by boiling the water or by the addition of lime (calcium hydroxide). Boiling promotes the formation of carbonate from the bicarbonate and precipitates calcium carbonate out of solution, leaving water that is softer upon cooling.
The following is the equilibrium reaction when calcium carbonate (CaCO3) is dissolved in water: CaCO3(s) + CO2(aq) + H2O ⇋ Ca2+(aq) + 2HCO3-(aq)
Upon heating, less CO2 is able to dissolve into the water (see Solubility). Since there is not enough CO2 around, the reaction cannot proceed from left to right, and therefore the CaCO3 will not dissolve as rapidly. Instead, the reaction is forced to the left (i.e., products to reactants) to re-establish equilibrium, and solid CaCO3 is formed. Boiling the water will remove hardness as long as the solid CaCO3 that precipitates out is removed. After cooling, if enough time passes, the water will pick up CO2 from the air and the reaction will again proceed from left to right, allowing the CaCO3 to "re-dissolve" into the water.
For more information on the solubility of calcium carbonate in water and how it is affected by atmospheric carbon dioxide, see calcium carbonate.

Permanent hardness

Permanent hardness is hardness (mineral content) that cannot be removed by boiling. It is usually caused by the presence in the water of calcium and magnesium sulfates and/or chlorides which become more soluble as the temperature rises. Despite the name, permanent hardness can be removed using a water softener or ion exchange column, where the calcium and magnesium ions are exchanged with the sodium ions in the column.
Hard water causes scaling, which is the left-over mineral deposits that are formed after the hard water had evaporated. This is also known as limescale. The scale can clog pipes, ruin water heaters, coat the insides of tea and coffee pots, and decrease the life of toilet flushing units.
Similarly, insoluble salt residues that remain in hair after shampooing with hard water tend to leave hair rougher and harder to untangle.
In industrial settings, water hardness must be constantly monitored to avoid costly breakdowns in boilers, cooling towers, and other equipment that comes in contact with water. Hardness is controlled by the addition of chemicals and by large-scale softening with zeolite (Na2Al2Si2O8.xH2O) and ion exchange resins.

Measurement
Because it is the precise mixture of minerals dissolved in the water, together with the water's pH and temperature, that determines the behavior of the hardness, a single-number scale does not adequately describe hardness. Descriptions of hardness correspond roughly with ranges of mineral concentrations: This scale is in substantial disagreement with the references.
|Very soft: |0-70 ppm |0-4 dGH |
|Soft: |70-140 ppm |4-8 dGH |
|Slightly hard: |140-210 ppm |8-12 dGH |
|Moderately hard: |210-320 ppm |12-18 dGH |
|Hard: |320-530 ppm |18-30 dGH |
|Very hard: |>530 ppm |>30 dGH |

It is possible to measure the level of total hardness in water by obtaining a total hardness water testing kit. These kits measure the level of calcium and magnesium in the water. Temporary hardness test kits do not normally measure calcium and magnesium levels but normally use an approximation based on some form of alkalinity test. Measuring temporary hardness accurately would involve a series of tests to work out how much bicarbonates and carbonates are present and how much calcium and magnesium is present and what percentage combination there is. In most cases, the temporary hardness kit is a good approximation, but anions such as hydroxides, borates, phosphates can have quite an effect on temporary hardness test kits.
There are several different scales used to describe the hardness of water in different contexts. • Parts per million (ppm) Usually defined as one milligram of calcium carbonate (CaCO3) per litre of water (the definition used below).[1] • grains per gallon (gpg) Defined as 1 grain (64.8 mg) of calcium carbonate per U.S. gallon (3.79 litres), or 17.118 ppm • mmol/L (millimoles per litre) One millimole of calcium (either Ca2+ or CaCO3) per litre of water corresponds to a hardness of 100.09 ppm or 5.608 dGH, since the molar mass of calcium carbonate is 100.09 g/mol. • Degrees of General Hardness (dGH) One degree of General Hardness is defined as 10 milligrams of calcium oxide per litre of water, which is the same as one German degree (17.848 ppm). • Various alternative "degrees": o Clark degrees (°Clark)/English degrees (°e or e) One degree Clark is defined as one grain (64.8 mg) of calcium carbonate per Imperial gallon (4.55 litres) of water, equivalent to 14.254 ppm. o German degrees (Deutsche Härte, °dH or dH) One degree German is defined as 10 milligrams of calcium oxide per litre of water. This is equivalent to 17.848 milligrams of calcium carbonate per litre of water, or 17.848 ppm. o French degrees (°f or f) (letter written in lower-case to avoid confusion with degree Fahrenheit — not always adhered to) One degree French is defined as 10 milligrams of calcium carbonate per litre of water, equivalent to 10 ppm. o American degrees One degree American is defined as one milligram of calcium carbonate per litre of water, equivalent to 1 ppm.
Although most of the above measures define hardness in terms of concentrations of calcium in water, any combination of calcium and magnesium cations having the same total molarity as a pure calcium solution will yield the same degree of hardness. Consequently, hardness concentrations for naturally occurring waters (which will contain both Ca2+ and Mg2+ ions), are usually expressed as an equivalent concentration of pure calcium in solution. For example, water that contains 1.5 mmol/L of elemental calcium (Ca2+) and 1.0 mmol/L of magnesium (Mg2+) is equivalent in hardness to a 2.5 mmol/L solution of calcium alone (250.2 ppm).

Indices

Several indices are used to describe the behaviour of calcium carbonate in water, oil, or gas mixtures.[2]

Langelier Saturation Index (LSI)

The Langelier Saturation Index (sometimes Langelier Stability Index) is a calculated number used to predict the calcium carbonate stability of water. It indicates whether the water will precipitate, dissolve, or be in equilibrium with calcium carbonate. In 1936, Wilfred Langelier developed a method for predicting the pH at which water is saturated in calcium carbonate (called pHs). The LSI is expressed as the difference between the actual system pH and the saturation pH: LSI = pH (measured) - pHs • For LSI > 0, water is super saturated and tends to precipitate a scale layer of CaCO3. • For LSI = 0, water is saturated (in equilibrium) with CaCO3. A scale layer of CaCO3 is neither precipitated nor dissolved. • For LSI < 0, water is under saturated and tends to dissolve solid CaCO3.
If the actual pH of the water is below the calculated saturation pH, the LSI is negative and the water has a very limited scaling potential. If the actual pH exceeds pHs, the LSI is positive, and being supersaturated with CaCO3, the water has a tendency to form scale. At increasing positive index values, the scaling potential increases.
In practice, water with an LSI between -0.5 and +0.5 will not display enhanced mineral dissolving or scale forming properties. Water with an LSI below -0.5 tends to exhibit noticeably increased dissolving abilities while water with an LSI above +0.5 tends to exhibit noticeably increased scale forming properties.
It is also worth noting that the LSI is temperature sensitive. The LSI becomes more positive as the water temperature increases. This has particular implications in situations where well water is used. The temperature of the water when it first exits the well is often significantly lower than the temperature inside the building served by the well or at the laboratory where the LSI measurement is made. This increase in temperature can cause scaling, especially in cases such as hot water heaters.

Ryznar Stability Index (RSI)

The Ryznar stability index (RSI) uses a database of scale thickness measurements in municipal water systems to predict the effect of water chemistry.
Ryznar saturation index (RSI) was developed from empirical observations of corrosion rates and film formation in steel mains. It is defined as: RSI = 2 pHs – pH (measured) • For 6,5 < RSI < 7 water is considered to be approximately at saturation equilibrium with calcium carbonate • For RSI > 8 water is under saturated and, therefore, would tend to dissolve any existing solid CaCO3 • For RSI < 6,5 water tends to be scale forming

Puckorius Scaling Index (PSI)

The Puckorius Scaling Index (PSI) uses slightly different parameters to quantify the relationship between the saturation state of the water and the amount of limescale deposited.

Other indices

Other indices include the Larson-Skold Index,[3] the Stiff-Davis Index,[4] and the Oddo-Tomson Index.[5]

Health considerations

The World Health Organization says that "there does not appear to be any convincing evidence that water hardness causes adverse health effects in humans."
Some studies have shown a weak inverse relationship between water hardness and cardiovascular disease in men, up to a level of 170 mg calcium carbonate per litre of water. The World Health Organization has reviewed the evidence and concluded the data were inadequate to allow for a recommendation for a level of hardness.[6]
In a review by František Kožíšek, M.D., Ph.D. National Institute of Public Health, Czech Republic there is a good overview of the topic which, unlike the WHO, sets some recommendations for the maximum and minimum levels of calcium (40-80 ppm) and magnesium (20-30 ppm) in drinking water, and a total hardness expressed as the sum of the calcium and magnesium concentrations of 2-4 mmol/L.[7]
Other studies have shown weak correlations between cardiovascular health and water hardness.[8][9][10]
A UK nationwide study, funded by the Department of Health, is investigating anecdotal evidence that childhood eczema may be correlated with hard water.[11]
Very soft water can corrode the metal pipes in which it is carried and as a result the water may contain elevated levels of cadmium, copper, lead and zinc.[6]

Softening

Main article: water softening
It is often considered desirable to soften hard water. This is because the calcium and magnesium causing hardness partly block the oil emulsifying action simple soap formulations use in the cleaning action. The calcium and magnesium form an insoluble precipitate observed as a soap scum and extra large amounts of soap have to be used to counteract this. Most modern soaps and detergents contain ingredients that at least partly prevent this effect and detergents are available that are chemically completely unaffected by the hardness. This makes hardness removal/softening an optional rather than a necessary water treatment except possibly in the case of extremely hard water. Where softening is practiced it is often recommended to soften only the water sent to domestic hot water systems so as to prevent or delay inefficiencies and damage due to scale formation in water heaters. Another reason for this is to avoid adding sodium or potassium from the softener to cold water taken for human consumption while still providing softening for hot water used in washing and bathing.

Process

A water softener works on the principle of cation or ion exchange in which ions of the hardness minerals (mainly calcium and magnesium ions) are exchanged for sodium or potassium ions, effectively reducing the concentration of hardness minerals to tolerable levels and thus making the water softer and giving it a smoother feeling.[12]
The most economical way to soften household water is with an ion exchange water softener. This unit uses sodium chloride (table salt) to recharge beads made of the ion exchange resins that exchange hardness mineral ions for sodium ions. Artificial or natural zeolites can also be used. As the hard water passes through and around the beads, the hardness mineral ions are preferentially absorbed, displacing the sodium ions. This process is called ion exchange. When the bead or sodium zeolite has a low concentration of sodium ions left, it is exhausted, and can no longer soften water. The resin is recharged by flushing (often back-flushing) with saltwater. The high excess concentration of sodium ions alter the equilibrium between the ions in solution and the ions held on the surface of the resin, resulting in replacement of the hardness mineral ions on the resin or zeolite with sodium ions. The resulting saltwater and mineral ion solution is then rinsed away, and the resin is ready to start the process all over again. This cycle can be repeated many times.
The discharge of brine water during this regeneration process has been banned in some jurisdictions (notably California, USA) due to concerns about the environmental impact of the discharged sodium.
Potassium chloride (softener salt substitute) may also be used to regenerate the resin beads. It exchanges the hardness ions for potassium. It also will exchange naturally occurring sodium for potassium resulting in sodium-free soft water.
Some softening processes in industry use the same method, but on a much larger scale. These methods create an enormous amount of salty water that is costly to treat and dispose of.
Temporary hardness, caused by hydrogen carbonate (or bicarbonate) ions, can be removed by boiling. For example, calcium bicarbonate, often present in temporary hard water, may be boiled in a kettle to remove the hardness. In the process, a scale forms on the inside of the kettle in a process known as "furring". This scale is composed of calcium carbonate. Ca(HCO3)2 → CaCO3 + CO2 + H2O
Hardness can also be reduced with a lime-soda ash treatment. This process, developed by Thomas Clark in 1841, involves the addition of slaked lime (calcium hydroxide — Ca(OH)2) to a hard water supply to convert the hydrogen carbonate hardness to carbonate, which precipitates and can be removed by filtration: Ca(HCO3)2 + Ca(OH)2 → 2CaCO3 + 2H2O
The addition of sodium carbonate also permanently softens hard water containing calcium sulfate, as the calcium ions form calcium carbonate which precipitates out and sodium sulfate is formed which is soluble. The calcium carbonate that is formed sinks to the bottom. Sodium sulfate has no effect on the hardness of water. Na2CO3 + CaSO4 → Na2SO4 + CaCO3

Effects on skin

Some confusion may arise after a first experience with soft water. Hard water does not lather well with soap and leaves a "clean" feeling. Soft water lathers better than hard water but leaves a "slippery feeling" on the skin after use with soap. Some providers of water softening equipment[13][14] claim that the "slippery feeling" after showering in soft water is due to "clean skin" and the absence of 'friction-causing' soap scum.
However, the chemical explanation is that softened water, because of its sodium content, has a much reduced ability to combine with the soap film on the body; therefore, the soap is much more difficult to rinse off.[15] Solutions are to use less soap or a synthetic liquid body wash.
Start your quality journey by mastering these tools, and you'll have a name for them too: "indispensable." 1. Cause-and-effect diagram (also called Ishikawa or fishbone chart): Identifies many possible causes for an effect or problem and sorts ideas into useful categories. 2. Check sheet: A structured, prepared form for collecting and analyzing data; a generic tool that can be adapted for a wide variety of purposes. 3. Control charts: Graphs used to study how a process changes over time. 4. Histogram: The most commonly used graph for showing frequency distributions, or how often each different value in a set of data occurs. 5. Pareto chart: Shows on a bar graph which factors are more significant. 6. Scatter diagram: Graphs pairs of numerical data, one variable on each axis, to look for a relationship. 7. Stratification: A technique that separates data gathered from a variety of sources so that patterns can be seen (some lists replace "stratification" with "flowchart" or "run chart").