Water Hardness and Alkalinity

CLASSIFICATION OF WATER HARDNESS

The amount of hardness is sometimes expressed by descriptive words. The following table shows how these descriptions may be related to the numerical value of the hardness in common units.

Description

Hardness in mg/l as
calcium

Hardness in mg/l as
calcium carbonate

Soft

Moderately soft

Slightly hard

Moderately hard

Hard

Very hard

0 – 20

20 – 40

40 – 60

60 – 80

80 – 120

Over 120

0 – 50

50 – 100

100 – 150

150 – 200

200 – 300

Over 300

(mg/l = milligrammes per litre = 1 part per million)

CONVERSION OF WATER HARDNESS UNITS

Water Hardness

Unit

 Difinition

International recommended

mmol/litre

Physical measures

mval/litre

America & states

PPM

English

oe

French

of

German

odH

100mg CaCO3

per 1000 ml water

28 mg CaO or 50 mg CaCO3

per 1000 ml water

1 part CaCO3 per million = 1 mg CaCO3

per 1000 ml water

1 grainCaCO3 per gallon= 14,3 mg CaCO3 per 1000 ml water

10 mg/ CaCO3

per 1000 ml water

10 mg/CaO

per 1000 ml water

1 mmol/litre

1 mval/litre

1 PPM

1 Oe

1 Of

1 OdH

1

0,5

0,01

0,1429

0,10

0,1786

2

1

0,02

0,285

0,20

0,357

100

50

1

14,29

10,00

17,86

7,0

3,5

0,070

1

0,700

1,250

10,00

5,00

0,10

1,429

1

1,786

5,6

2,8

0,056

0,7999

0,5599

1

WATER H2O HARDNESS

TEMPORARY HARDNESS: Ca AND Mg BICARBONATES (precipitate minerals upon heating)

PERMANENT HARDNESS: Ca AND Mg SULFATES OR CHLORIDES (dissolve with sodium)

DEGREE OF HARDNESS EXPRESION. PPM Calcium (US norm), odH (European norm*)

SOFT: LESS THAN 1,6 mmol/l = 160 PPM = 9 odH

SLIGHTLY HARD: 1,6-3,2 mmol/l = 160-320 PPM = 9-18 odH

HARD: 3,2-4,6 mmol/l = 320-460 PPM = 18-26 odH

VERY HARD: ABOVE 4,6 mmol/l = ABOVE 460 PPM = ABOVE 26 odH

1 odH = 10 mg/CaO = 17,8 mg/l CaCO3 = 0,18 mmol/l earth alkaline ions

(* 1 odH = 17,86 PPM American hardness = 1,25 o English hardness = 1,78 o French hardness)

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