Hardness was originally defined as the capacity of water to precipitate soap.
Hardness of water is due to the presence of calcium and magnesium salts: bicarbonates, carbonates, chlorides, sulphates and nitrates. Presence of iron, aluminium and manganese salts also contributes to water hardness, but normally these are not present in appreciable quantities. Normal carbonates are also found, but only occasionally and in highly alkaline water. Nitrates are usually present in minor quantities while it has been found that sulphates on the average exceed chlorides.
Removing hardness from water is called softening and hardness is mainly caused by calcium and magnesium salts. These salts are dissolved from geologic deposits through which water travels. The length of time water is in contact with hardness producing material helps determine how much hardness there is in raw water.
The two basic methods of softening public water supplies are chemical precipitation and ion exchange. Other methods can also be used to soften water, such as electro dialysis, distillation, freezing, and reverse osmosis. These processes are complex and expensive and usually used only in unusual circumstances
The two basic methods of softening public water supplies are chemical precipitation and ion exchange. Other methods can also be used to soften water, such as electro dialysis, distillation, freezing, and reverse osmosis. These processes are complex and expensive and usually used only in unusual circumstances
As you can see boiling the water causes the precipitation of solid calcium carbonate or solid magnesium carbonate. This removes the calcium ions or magnesium ions from the water, and so removes the hardness. Therefore, hardness due to hydrogen carbonates is said to be temporary.
Hard water forms scale, usually calcium carbonate, which causes a variety of problems. Left to dry on the surface of glassware, silverware, and plumbing fixtures (shower doors, faucets, and sink tops), hard water leaves an unsightly scale called water spots. Scale that forms inside water pipes eventually reduces water pipe carrying capacity. Scale that forms within appliances, pumps, valves, and water meters causes wear on moving parts.
When hard water is heated, scale forms much faster. This creates an insulation problem inside boilers, water heaters, and hot-water lines, and increases water heating costs.
Hardness limit:
Soft: 0 to70 mg/L as CaCO3
Moderate: 70 to 150 mg/L as CaCO3
Hard: 150 to 300 mg/L as CaCO3
Very Hard: Above 300 mg/L as CaCO3
Although strontium, aluminum, barium, iron, manganese, and zinc also cause hardness in water, they are not usually present in large enough concentrations to contribute significantly to total hardness.
Water hardness is unfortunately, expressed in several different units and it is often necessary to convert from one unit to another when making calculations. Most commonly used units include grains per gallon (gpg), parts per million (ppm), and milligrams per liter (mg/L).