A glossary of hard water terms and terminology

Hard water

Hard water is any water that has a high mineral content, such as calcium and magnesium. These minerals enter the water as a result of percolation through limestone or chalk rocks. The greater the number of dissolved minerals, the harder the water.

Soft water

Soft water is any water that has a low mineral content. Rainwater is naturally soft before the weathering process causes the water to become hard. It is also possible to get soft water from water softening.

Softened water

Softened water refers to any hard water that has been through a water-softening process. This process involves removing the calcium and magnesium ions in exchange for sodium or potassium ions.

Limestone

Limestone is a carbonate sedentary rock, primarily made of calcium carbonate, that is dissolvable in water. Limestone is one of the biggest factors contributing towards hard water. As limestone contains horizontal layers (or bedding planes) and vertical cracks (joints), it is possible for rainwater to pass through.

Limescale

Limescale is a hard, chalky deposit that is primarily caused by calcium carbonate. This occurs when the calcium ions in hard water react with carbonate ions. Limescale forms when boiling water or leaving it to evaporate on a hard surface.

Scale deposits

Scale deposits are another term for limescale and are a typical indicator of hard water.

Carbonates

Carbonate refers to any chemical compound that has carbonate ions present. Typically, carbonate ions have a -2 charge and will form salts and minerals when combined with metal cations. An example of a metal cation is calcium carbonate.

Bicarbonates

Bicarbonates are a chemical compound that contains bicarbonate ions. Dissolved bicarbonate minerals are a cause of temporary hardness. Softened water will also contain higher levels of bicarbonate ions.

Sulfate

Sulfate or sulphates refer to a group of mineral salts that can either be naturally or artificially made. These salts typically appear in water as a result of household waste or industrial runoff. The presence of calcium sulfate or magnesium sulfate contributes to permanent water hardness.

Water softening

Water softening is the process of removing permanent water hardness. This process removes the calcium, magnesium, and metal cations found in the water. This can either be achieved by the addition of sodium carbonate or the ion-exchange process.

Water conditioning

Water conditioning is a method used for treating hard water. A range of different processes can be used, such as magnetic, electrolytic, or electrostatic, to change the properties of hardness molecules. As such, this prevents them from sticking to hard surfaces and forming limescale. An example of a water conditioning method is using an electronic water descaler.

Precipitation

Precipitation is a part of the weather process, whereby water falls from clouds as rain or snow towards the ground. It can also be a chemical process that results in a substance to precipitate.

Ions

An ion is a molecule or atom that has a net electrical charge (one or more positive or negative electrical charges). Permanent water hardness is determined by the concentration of cations (or ions) that have a charge greater than or equal to 2+. The most common of these cations found in hard water are Ca2+ (calcium ions) and Ma2+ (magnesium ions).

Cations

Cations are any ions that have a positive charge.

Anions

Anions are any ions that have a negative charge.

Calcium carbonate

Calcium carbonate is a result of calcium ions reacting with carbonate ions that create limescale. As this mineral is less soluble in hot water, it becomes solid to form limescale. It’s also a common substance found in rocks.

Calcium bicarbonate

Calcium bicarbonate contributes to temporary hardness in water. It is not a solid compound and can only be found in aqueous solutions that contain calcium, bicarbonate, and carbonate ions.

Permanent hardness

Permanent hardness is any water that remains hard after boiling. This is because the sulfates in hard water do not decompose easily. The only way to remove permanent hardness is through water softening.

Temporary hardness

Temporary hardness is any water that can be boiled to remove hardness. Bicarbonate salts of calcium and magnesium are the cause of temporary hardness. This is done by decomposing bicarbonates back into insoluble carbonates.

Ion exchange

Ion exchange is a treatment process for softening water. This process removes calcium and magnesium ions from hard water and replaces them with sodium or potassium ions. This is done using a resin, typically lots of resin beads inside the water softener.

Lime softening

Lime softening is a chemical process that seeks to reduce water hardness with the addition of lime. This helps to precipitate calcium and magnesium as solids. Lime softening can sometimes be called Clark’s process.

Soap scum

Soap scum is a white, chalky residue similar to limescale stains. This residue is usually insoluble, and forms as a result of soap reacting with the calcium and magnesium present in hard water.

Calcium stearate

Calcium stearate is the main component of soap scum. It is not insoluble in water and is difficult to lather. Despite this, it has main uses and can be used as a flatting agent in paint, a thickener in cosmetics, and a lubricant for industrial use.

pH

pH (short for potential of hydrogen) is a logarithmic scale to measure the acidity or alkalinity of a solution. Drinking water usually has a neutral pH of 7. However, calcium and magnesium minerals can affect acids in the water, leading to a higher pH level.

Sodium carbonate

Sodium carbonate (sometimes called washing soda) can be used to precipitate calcium and magnesium ions from hard water. It can sometimes be added to laundry water to help soften it.

Parts per million (PPM)

Parts per million (abbreviated to PPM) is a measurement of the total concentration of calcium and magnesium ions in water. 1 PPM is equal to 1 mg/L of CaCo3 or calcium carbonate. The greater the PPM, the greater the hardness.

Mmol/L

Mmol/L is a measurement, short for millimoles per litre. This measurement is used for the amount of calcium carbonate in water.

Atopic dermatitis

Atopic dermatitis (or eczema) is a condition that affects the skin. It can cause dry, itchy, or bumpy skin that is prone to rashes, blisters, and bleeding due to the weakening of the skin’s barrier. There is strong evidence to suggest that children living in hard water areas are more likely to develop eczema and adults can experience worsening symptoms.

Degree Clark

Degree Clark is an imperial measurement of hard water. While not as widely used as other metrics nowadays, you may still come across it. 1 degree Clark is roughly equivalent to 17.1 parts per million.

Total dissolved solids (TDS)

Total dissolved solids (or TDS) is another metric used to measure impurities in water. It is generally used for measuring the minerals, salts, and other organic compounds that dissolve naturally into water.

Scaling

Deposits of calcium carbonate and magnesium hydroxide that build up inside pipes, boilers, and appliances. This can have a big impact on the efficiency and lifespan of appliances and heating systems.

By better understanding the meaning behind hard water terms and terminology, you are in a much better position to find the best possible solution to combating its effects. Whether you experience problems with your skin or hair or scale build-up, we hope our glossary made certain terms or terminology clearer.