Hard water
Natural rainwater, snow and other forms of precipitation typically have low concentrations of divalent cations such as calcium and magnesium.
They may have small concentrations of ions such as sodium, chloride and sulfate derived from wind action over the sea.
Areas with complex geology can produce varying degrees of hardness of water over short distances.
[3] Calcium and magnesium carbonates tend to be deposited as off-white solids on the inside surfaces of pipes and heat exchangers.
[10] The damage caused by calcium carbonate deposits varies according to the crystalline form, for example, calcite or aragonite.
The solubility of the hydroxides of the alkaline-earth metals to which calcium and magnesium belong (group 2 of the periodic table) increases moving down the column.
Hence, a common solution to the problem is, while maintaining the chlorine concentration at the proper level, to lower the pH by the addition of hydrochloric acid, the optimum value is in the range of 7.2 to 7.6.
Washing soda (sodium carbonate, Na2CO3) is easily obtained and has long been used as a water softener for domestic laundry, in conjunction with the usual soap or detergent.
[2] In fact, the United States National Research Council has found that hard water serves as a dietary supplement for calcium and magnesium.
The World Health Organization has reviewed the evidence and concluded the data was inadequate to recommend a level of hardness.
[18][19] Living in areas with hard water may also play a part in the development of AD in early life.
Although water hardness usually measures only the total concentrations of calcium and magnesium (the two most prevalent divalent metal ions), iron, aluminium, and manganese are also present at elevated levels in some locations.
[22] Several indices are used to describe the behaviour of calcium carbonate in water, oil, or gas mixtures.
In 1936, Wilfred Langelier developed a method for predicting the pH at which water is saturated in calcium carbonate (called pHs).
If the actual pH exceeds pHs, the LSI is positive, and being supersaturated with CaCO3, the water tends to form scale.
Total hardness levels of calcium carbonate in ppm are: Prairie provinces (mainly Saskatchewan and Manitoba) contain high quantities of calcium and magnesium, often as dolomite, which are readily soluble in the groundwater that contains high concentrations of trapped carbon dioxide from the last glaciation.
The west coast, by contrast, has unusually soft water, derived mainly from mountain lakes fed by glaciers and snowmelt.
Some typical values are: Information from the Drinking Water Inspectorate shows that drinking water in England is generally considered to be 'very hard', with most areas of England, particularly east of a line between the Severn and Tees estuaries, exhibiting above 200 ppm for the calcium carbonate equivalent.
Wales, Devon, Cornwall, and parts of northwest England are softer water areas and range from 0 to 200 ppm.
[58] In the brewing industry in England and Wales, water is often deliberately hardened with gypsum in the process of Burtonisation.
Several cities built water supply sources in the 18th century as the Industrial Revolution and urban population burgeoned.
[52] Similarly, tap water in Birmingham is also soft as it is sourced from the Elan Valley Reservoirs in Wales, even though groundwater in the area is hard.
The handbook does indicate that above the midpoint of the ranges defined as "Moderately Hard", effects are seen increasingly: "The chief disadvantages of hard waters are that they neutralise the lathering power of soap [...] and, more important, that they can cause blockage of pipes and severely reduced boiler efficiency because of scale formation.
[citation needed] The softest waters occur in parts of the New England, South Atlantic–Gulf, Pacific Northwest, and Hawaii regions.
Moderately hard waters are common in many of the rivers of the Tennessee, Great Lakes, and Alaska regions.
