What Is Hard Water? Origin, Types & Hardness Measurement Methods

Hard water is water that has a lot of minerals in it, like calcium and magnesium. It happens when water goes through rocks like limestone or chalk. Hard water might be okay to drink in moderation, but it can cause big problems in factories and machines that use water. In homes, you can tell if you have hard water because soap doesn’t make much foam, and you get that white, crusty stuff in kettles and water heaters. To fix these issues, people often use different softeners to make the water less hard.

Origins

Where rain, snow, and similar forms of water from the sky start, they usually don’t have a lot of minerals like calcium and magnesium. Sometimes, they can pick up a bit of salt and other things from the sea because of the wind. But when this water falls in areas with rocks that don’t have much calcium and can’t absorb water well, it stays low in minerals and is called soft water. Some places like Snowdonia in Wales and the Western Highlands in Scotland have this kind of soft water.

Types of hard water

Hard water contains a high concentration of dissolved minerals, primarily calcium and magnesium ions. These minerals can cause various issues in households and industrial settings. There are two main types of hard water:

Temporary Hard Water:

Temporary hardness is caused by the presence of bicarbonate ions (HCO3-) in the water, primarily as calcium bicarbonate (Ca(HCO3)2) and magnesium bicarbonate (Mg(HCO3)2). It can be removed or reduced by boiling the water or by adding chemicals such as lime (calcium hydroxide) or soda ash (sodium carbonate). When you boil temporary hard water, the bicarbonate ions decompose, forming insoluble carbonate solids and releasing carbon dioxide gas. The resulting calcium and magnesium carbonates settle out, making the water softer.

Permanent Hard Water:

Permanent hardness is caused by the presence of calcium sulfate (CaSO4), magnesium sulfate (MgSO4), or other non-bicarbonate minerals in the water. Unlike temporary hardness, permanent hardness cannot be removed by boiling alone. It requires the use of water softeners or ion-exchange resins to remove the calcium and magnesium ions from the water and replace them with sodium ions.

Effects of hardness

Water hardness, whether temporary or permanent, can have various effects on both domestic and industrial settings. Here are some of the common effects of water hardness:

Scale Formation:

Hard water can lead to the accumulation of mineral deposits, primarily calcium and magnesium carbonate, on plumbing fixtures, pipes, and appliances. This buildup, known as scale or limescale, reduces water flow, decreases the efficiency of water heaters and boilers, and can ultimately lead to clogs and damage if left untreated.

Reduced Soap Lathering:

Hard water can react with soap to form soap scum or curd. This makes it difficult to produce a lather and can result in soap and detergent not cleaning as effectively. As a result, you may need to use more soap or detergent to achieve the desired cleaning results.

Increased Energy Consumption:

When water heaters and boilers have scale buildup due to hard water, they become less efficient. This means they require more energy to heat water, leading to higher energy bills.

Appliance Damage:

Household appliances that use water, such as dishwashers, washing machines, and coffee makers, can be negatively affected by hard water. Scale can accumulate in these appliances, leading to reduced performance and a shortened lifespan.

Clogged Pipes:

Over time, hard water can lead to the narrowing of water pipes due to scale buildup. This can result in reduced water flow and increased maintenance costs for plumbing systems.

Skin and Hair Issues:

Hard water can leave a residue on your skin and hair, making it feel dry and less smooth. It can also make it more challenging to rinse out shampoo and soap completely, potentially causing skin irritations and dull, lifeless hair.

Read Our Guide: Hard Water Hair

Stained Fixtures and Dishes:

The minerals in hard water can cause stains on dishes, glassware, and bathroom fixtures like sinks and bathtubs, which can be unsightly and difficult to remove.

Increased Laundry Detergent Use:

Hard water requires more laundry detergent to achieve the same level of cleaning, which can increase laundry costs over time.

Negative Impact on Industrial Processes:

In industrial settings, hard water can interfere with various processes, including cooling systems, manufacturing processes, and water-based chemical reactions. This can lead to reduced efficiency, increased maintenance, and higher operational costs.

To mitigate the effects of water hardness, many people and businesses install water softeners or use other water treatment methods to reduce the concentration of calcium and magnesium ions in the water. Softened water is often preferred for its ability to prevent scale formation, improve cleaning and lathering, and extend the lifespan of appliances and plumbing systems.

Hardness Measurement

Water hardness is typically measured in units known as “grains per gallon” (gpg) or milligrams per liter (mg/L), also equivalent to parts per million (ppm). There are two primary methods for measuring water hardness:

Titration Method:

This method involves titrating a water sample with a standard solution of a chemical reagent that reacts with the calcium and magnesium ions in the water. The most common reagents used for this purpose are ethylenediaminetetraacetate (EDTA) and complexometric indicators. The titration process continues until a color change occurs, indicating the endpoint of the reaction. The volume of the titrant needed to reach the endpoint is then used to calculate the hardness of the water in grains per gallon or milligrams per liter.

Test Strips or Test Kits:

Test strips or test kits are simpler and more convenient for quick, on-site measurements of water hardness. These kits typically contain paper or plastic strips impregnated with chemicals that change color when exposed to hard water. Users dip the test strip into the water sample and then compare the resulting color change to a color chart provided with the kit to determine the hardness level. This method provides a rough estimate of water hardness and is suitable for home use and quick assessments.

Here are the general conversions between different units for measuring water hardness:

• 1 grain per gallon (gpg) is approximately equal to 17.1 milligrams per liter (mg/L).
• 1 milligram per liter (mg/L) is equivalent to 1 part per million (ppm).

Water hardness can differ by location, so it’s wise to check it occasionally, especially if it affects your plumbing, appliances, or cleaning. For precise measurements for tasks like industry or labs, the titration method is preferred for its accuracy. For everyday purposes and quick assessments, test strips or test kits can provide a reasonably accurate estimate of water hardness.

Read Also: What is the Ideal Water Hardness Level

Hardness unit conversion.

Converting between different units of water hardness can be useful when you encounter measurements expressed in grains per gallon (gpg), milligrams per liter (mg/L), or parts per million (ppm).

	1 mmol/L	1 ppm, mg/L	1 dGH, °dH	1 gpg	1 °e, °Clark	1 °fH
mmol/L	1	0.009991	0.1783	0.171	0.1424	0.09991
ppm, mg/L	100.1	1	17.85	17.12	14.25	10
dGH, °dH	5.608	0.05603	1	0.9591	0.7986	0.5603
gpg	5.847	0.05842	1.043	1	0.8327	0.5842
°e, °Clark	7.022	0.07016	1.252	1.201	1	0.7016
°fH	10.01	0.1	1.785	1.712	1.425	1

Hard/soft classification

Water hardness is typically classified into different categories based on the concentration of calcium and magnesium ions in the water. The classification can vary slightly depending on the source, but here’s a general classification commonly used in the United States and some other regions:

Soft Water

0 to 60 mg/L (milligrams per liter) or ppm (parts per million) of calcium carbonate (CaCO3) equivalent: Water in this range is considered soft. Soft water typically does not cause scaling issues or soap scum buildup. It lathers easily with soap and is gentle on skin and hair.

Slightly Hard Water

61 to 120 mg/L or ppm of calcium carbonate equivalent: Water in this range is considered slightly hard. It may have a mild tendency to cause scaling in appliances and pipes but is still relatively gentle on skin and appliances. Soap lathering is usually not significantly affected.

Moderately Hard Water

121 to 180 mg/L or ppm of calcium carbonate equivalent: Water in this range is moderately hard. It can lead to noticeable scale buildup in pipes and appliances over time. Soap may not lather as well, and it might be necessary to use more soap or detergent for effective cleaning.

Hard Water

181 to 250 mg/L or ppm of calcium carbonate equivalent: Water in this range is considered hard. It is likely to cause scale buildup in plumbing and appliances. Soap lathering is noticeably reduced, and soap scum may be more prominent.

Very Hard Water

Over 250 mg/L or ppm of calcium carbonate equivalent: Water in this range is considered very hard. It can lead to severe scale problems in plumbing and appliances. Soap lathering is significantly affected, and a considerable amount of soap or detergent may be required for cleaning.

Hardness water level of major cities in England and Wales

water hardness levels in a few major cities in England and Wales. Please note that these values are approximate and can change over time:

• London: Water hardness in London can vary depending on the specific area within the city. It generally falls in the range of moderately hard to hard, with hardness levels around 150-200 mg/L (ppm CaCO3 equivalent).
• Manchester: Manchester and its surrounding areas often have moderately hard, with hardness levels ranging from 60 to 120 mg/L (ppm CaCO3 equivalent).
• Birmingham: Birmingham and the West Midlands can have varying hardness levels, but it’s typically in the moderately hard, with levels around 100-200 mg/L (ppm CaCO3 equivalent).
• Cardiff (Wales): Cardiff’s water supply can have varying levels of hardness, but it’s generally classified as moderately hard, with levels around 100-150 mg/L (ppm CaCO3 equivalent).
• Bristol: Bristol’s water supply is known for its hardness, falling in the hard water category with levels typically above 150 mg/L (ppm CaCO3 equivalent).

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Water hardness in the United States

Water hardness in the United States varies widely depending on the specific region and local water sources. The United States Geological Survey (USGS) has categorized different areas of the country based on their typical water hardness levels. Water hardness depends on major-ion chemistry, which remains steady in groundwater and doesn’t change much over time. Despite the data being from 1975, they are reliable and offer insights for today’s assessments.

• The data shown reflect water hardness at a national and regional level and should be understood in that context.
• The data from 1975 are not intended for making local or individual homeowner decisions.
• For precise information regarding water hardness and other chemical properties specific to a home or immediate area, it’s best to consult the local health agency, the local water utility, or a local water-softening system vendor.