Hardness in water
Originally described as water’s capacity to precipitate soap, hardness is one of the most frequently determined qualities of water. It is a composite of the calcium, magnesium, strontium and barium concentrations in a sample. The current practice is to assume total hardness refers to the calcium and magnesium concentrations only.
Completely de-hardened water, resulting from sodium zeolite or other suitable ion exchange treatment, is required for various processes-including power generation, printing and photo finishing, pulp and paper manufacturing, and food and beverage processing.
Hard water can cause scale formation on heat exchange surfaces resulting in decreased heat transfer and equipment damage.
For example, sometimes the pipes in our homes get clogged because precipitates of magnesium and calcium oxides have deposited themselves within the pipes. This can happen with “hard” water. Another example is a kidney stone. A kidney stone is nothing more than a precipitate – often of calcium ions (from cheese) and oxalates. It is often suggested that a good way to avoid kidney stones is to drink a lot of water. This helps because the solubility of the precipitate increases with the amount of water – thus avoiding the formation of the kidney stone to begin with .
Water Hardness
Water hardness is generally expressed as a concentration of calcium carbonate, in terms of milligrams per liter as CaCO3. The degree of hardness that consumer consider objectionable will vary, depending on other qualities of the water and on the hardness to which they have become accustomed.
CLASSIFICATION mg/l CaCO3
Soft 0 – 75
Moderately hard 75 – 150
Hard 150 – 300
Very hard Over 300
Problems in the Home from Hard Water
Scale Formation
Hard water forms scale, usually calcium carbonate, which causes a variety of problems. Left to dry on the surface of glassware and plumbing fixtures, including showers doors, faucets, and sink tops, hard water leaves unsightly white scale known as water spots. Scale that forms on the inside of water pipes will eventually reduce the flow capacity or possibly block it entirely. Scale that forms within appliances and water meters causes wear on moving parts.
A coating of only 0.04 in. (1mm) of scale on the heating surfaces of a hot water heater creates an insulation effect that will increase heating costs by about 10 percent.
Objections to hardness in water
has been its effect on soap. Hardness ions form precipitates with soap. Causing unsightly “curd,” such as the familiar bathtub ring, as well as reduced efficiency in washing and laundering. To counteract these problems, synthetic detergents have been developed and are now used almost exclusively for washing clothes and dishes.
These detergents have additives known as sequestering agents that “tie up” the hardness ions so that they cannot form the troublesome precipitates. Although modern detergents counteract many of the problems of hard water, many customers prefer softer water.