Chemistry of Hard vs Soft Water and Why it Matters?

Since water comes from different sources, the quality of water in a region can vary considerably from other regions. Water accumulates dissolved solids as it moves. Depending on the geographical area, water may contain calcium, magnesium, sodium, and other minerals.

Water is categorized into two types depending upon the presence of mineral content: hard water and soft water.

“Hard water contains an appreciable amount of calcium, magnesium, iron, and manganese ions usually in the form of bicarbonates, chlorides, and sulfates. While soft water has a minute amount of calcium and magnesium ions but contains sodium ions in appreciable amount.”

In order to categorize water as soft or hard water, the amount of calcium carbonate in milligrams per liter (mg/L) or also called parts per million (ppm) is measured. The below points can be used to categorize water as soft or hard, once the amount (mg/L) of CaCO3 is known.

  • 0 to 60 mg/L = Soft water water
  • 60 to 120 mg/L = Moderately hard water
  • 120 to 180 mg/L = Hard water
  • 180 mg/L and over = Very hard water

Hard Water vs Soft Water

Hard water Soft water
Hard water is rich in minerals Soft water contains fewer minerals
It mainly has calcium and magnesium ions It mainly contains sodium ions
Calcium carbonate concentration in hard water is more than 60 mg/L (ppm) Calcium carbonate concentration in soft water is less than 60 mg/L (ppm)
Hard water forms insoluble curds with soap rather than lather Soft water forms good lather with soap
It is not suitable for washing dishes as it leaves spots once dried Soft water is suitable for washing the dishes
It makes skin and hairs dry It does not affect any hairs and skin
It is not suitable for boilers and other machines It is suitable for boilers and other machines
Water becomes hard when it moves through limestone, gypsum, chalk, and other rocks Igneous, sedimentary rocks and sand stone have soft water. Rainwater is soft as well.
Water can be made hard by dissolution of calcium and magnesium salts Soft water can be produced by treating hard water with a suitable ion exchange resin
Hard water has a characteristic chemical taste Soft water has a bit salty taste
It causes deposition of calcium and magnesium salts in pipes, taps, and machines It does not cause any deposition in pipes, taps, and machines

Drinking Hard and Soft Water

Hardness does not pose any health risk and is, therefore, not regulated in the world. In fact, calcium and magnesium in hard water can ensure one’s daily requirement for these minerals.

In 1971, WHO International Standards for Drinking water stated that the maximum level of hardness in drinking water is 500 mg/L of calcium carbonate (10 mEq/L).

However, the first edition of the Guidelines for Drinking Water Quality, published in 1984, concluded that there was no firm evidence that drinking hard water causes any adverse effects on human health and that no recommendation on the restriction of municipal water softening or on the maintenance of minimum residual calcium or magnesium level was given.

A guideline value of 500 mg/liter (as calcium carbonate) was established for hardness, based on taste and household use considerations. No health-based guideline value for hardness was proposed in the 1993 Guidelines, although hardness above approximately 200 mg/liter may cause scale deposition in the distribution system over time.

Drinking too much soft water isn’t the best choice either, as soft water indicates higher sodium content. High sodium content may not be good to drink and may have an adverse effect on those following a low sodium diet due to high blood pressure. The solution, therefore, is to find a balance of the mineral content.

Impact of water hardness

Although hard water does not have any health concerns, it can be a nuisance as it interferes with almost every cleaning task, from doing the laundry to washing dishes and taking a shower.

  • Hard water makes clothes feel rough and scratchy, shortening their lives.
  • Spots may appear on dishes after drying.
  • Hairs become dull.
  • Hard water leaves residue buildup in pipes, sinks, faucets, bathtubs, etc making them clog.
  • The cost of water heating gets raised as hard water is difficult to boil.
  • The efficiency of boilers get lowered after some time.

How to test the hardness of water?

Water hardness can be easily checked using a simple test.

Take an empty bottle and add the sample water. Make sure half of the bottle is still empty. Now add pure liquid soap (a few drops) to that bottle and shake, so that soap turns into bubbles. The lesser the bubbles formed, the harder your water is. This test can only predict a general view of the hardness of water. So, in order to quantify the hardness level of water, a hard water test kit is required.

A hard water test kit works just like a pH paper. It is dipped in sample water for a few minutes and then its color is matched to a standard color list. This test gives you the hardness of water in Grains per gallon (GPG).

Softening of Hard water

A process in which calcium magnesium, and sometimes, iron and manganese ions are removed from water is termed softening of hard water. Turning hard water into soft water can be achieved by the following processes.

  1. Boiling hard water (some salts precipitate upon boiling)
  2. Chemical treatment (Adding chemicals to produce insoluble precipitates, thus lowering water hardness). These chemicals include:
    1. Ammonia
    2. Borax
    3. Slaked lime
    4. Sodium carbonate
  3. Ion exchange (An industrial method that uses ion exchange resins in column forms). The resins include:
    1. Natural aluminosilicate
    2. Zeolite, etc

Key Differences Between Hard and Soft Water

Difference between hard and soft water

Concepts Berg

Is hard water bad for you?

Millions of people rely on hard water which contains high concentrations of dissolved minerals. The dissolved minerals seem to be beneficial for those consuming the water.

How does hard water affect your shower?

Having a shower with hard water will make your skin and hair dry.

What are the benefits of soft water?

Soft water is the best option for laundry and washing dishes.

What is water softening?

Water softening is the process of removing the dissolved calcium and magnesium salts that cause hardness in water. It is done by an ion exchange resin.

How can you prevent hard water stains?

Wipe your dishes and utensils with a soft cloth after washing with hard water. This will remove the water on the surface and prevent mineral deposition.

Soft vs. hard water: Which is better for drinking?

Both soft and hard water are good to drink. However, finding a balance of the mineral content would be more appropriate.

What is a disadvantage of soft water?

Continuous drinking of soft water increases a person’s sodium levels which can lead to multiple health problems including high blood pressure.

What is the difference between soft water and distilled water?

Distilled water has all of the minerals and impurities removed. Whereas soft water has only calcium and magnesium ions removed.

What is the difference between soft water and deionized water?

Deionized water does not have any nutritional value whereas, soft water contains some minerals.

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