WATER HARDNESS

 

Water is an very good solvent and readily dissolves minerals it comes in contact with. As water moves through soil and rock, it dissolves very small amounts of minerals (like Ca⁺² and Mg⁺²) and holds them in solution.

Water hardness is defined the sum of equivalent concentration of the Calcium and Magnesium ions in water.

The classification of water according to hardness is given in below table

mg Ca+2/l	mg CaCO3/l	French Degrees	German Degrees	Hardness
<30	<75	<7.5	<4.2	Very soft
30-50	75-125	7.5-12.5	4.2-7.0	Soft
50-100	125-250	12.5-25.0	7.0-14.0	Moderate hard
100-150	250-375	25.0-37.5	14.0-21.0	Hard
>150	>375	>37.5	>21.0	Very hard

 

Forms of Hardness

There are two forms of hardness: temporary and permanent. Temporary hardness is the portion of the total hardness that is associated with alkalinity. Permanent hardness is all of the rest. The term ‘temporary hardness’ is a result of the reversibility of the calcium carbonate precipitation reaction with heat. Heating a solution ‘temporarily’ precipitates the hardness; cooling re-dissolves it. Permanent hardness, on the other hand, is not removed by heating.

Advantages of Hardness Removal

• Smaller amount of dish washing and laundry detergent is needed.
• Reduced mineral deposits in plumbing, water heaters, and on pots and pans.
• Fewer water spots on air-dried dishes and glassware.
• Hair and skin will often feel softer after bathing or washing.

What are the health effects of Hardness?

Hardness does not pose a health risk. In fact, calcium and magnesium in your drinking water can help ensure you get the average daily requirements for these minerals in your diet. There are no Standard for Hardness.

Hardness Removal Methods

• Ion exchange softening
• Reverse-osmosis
• Nanofiltration
• Electrodialysis
• Distillation
• Lime Soda Process