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2002

By Authority Of
THE UNITED STATES OF AMERICA
Legally Binding Document
By the Authority Vested By Part 5 of the United States Code § 552(a) and
Part 1 of the Code of Regulations § 51 the attached document has been duly
INCORPORATED BY REFERENCE and shall be considered legally
binding upon all citizens and residents of the United States of America.
HEED THIS NOTICE: Criminal penalties may apply for noncompliance.

e
Document Name: ASTM D-1126 (2002): Standard Test Method for
Hardness in Water

CFR Section(s):
40 CFR 136.3(a)

Date of Action: 67 FR 69971, Nov. 19, 2002

Official Incorporator:
THE EXECUTIVE DIRECTOR
OFFICE OF THE FEDERAL REGISTER
WASHINGTON, D.C.

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INTERNATIONAL
Designation: D 1126-02

Standard Test Method for

Hardness in Water 1
standard .is issU(:d under the fixed designation D 1126; the number immediately following the designation indicates the year of
T ~ i s .

ongmal adoption or, m the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.

This standard has been approved for use by agencies of the Depal'fmellt of Defense.

1. Scope refer to Terminology D 1129.

1.1 This test method covers the determination of hardness in
4. Summa ry of Test Method
water by titration. This test method is applicable to waters that
are clear in appearance and free of chemicals that will complex 4.1 Calcium and magnesium ions in water are sequestered
calcium or magnesium. The lower detection limit of this test by the addition of disodium ethylenediamine tetraacetate. Th e
method is approximately 2 to 5 mg/L as CaC0 3 ; the upper limit end point of the reaction is detected by means of Chrome Black
can be extended to all concentrations by sample dilution. It is T , which has a red color in the presence of calcium and
magnesium and a blue color when they are sequestered.
possible
and that toduedifferentiate
to magnesiumbetween hardness
ions by duemethod.
this test to calcium ions
5. Significance an d Use
1.2 This test method was tested on reagent water only. I t is
the user's responsibility to ensure the validity of the test 5.1 Hard ness salts in water, notably calcium an d magne
method for waters of untested matrices. . sium, are the primary cause of tube and pipe scaling, which
1.3 This standard does not purport to address all o f the frequently causes failures and loss of process efficiency due to
safety concerns, if any, associated with its use. It is the clogging or loss of heat transfer, or both.
responsibility of the user o f this standard to establish appro 5.2 Hardness is caused by any polyvalent cations, bu t those
priate safety and health practices and determine the applica other than Ca and Mg are seldom present in more than trace
bility o f regulatory limitations prior to use. amounts. Th e term hardness was originally applied to water in
which it was hard to wash; it referred to the soap-wasting
2. Referenced Documents properties of water. With most normal alkaline water, these
2.1 ASTM Standards: soap-wasting properties are directly related to the calcium and
D 1066 Practice for Sampling Steam2 magnesium content.
D 1129 Terminology Relating to Water2
6. Interferences
D 1193 Specification for Reag ent Water2
D 3370 Practices for Sampling Water from Closed Con 6.1 Th e substances shown in Table 1 represent the highest
duits 2 concentrations that have been found not to interfere with this
D 5847 Practice for Writing Quality Control Specifications determination.
for Standard Test Methods for Water Analysis 3 6.2 The test method is not suitable for highly colored
waters, which obscure the color change of the indicator.
3. Terminology
7. Reagents
3.1 Definitions:
3.1.1 equivalent per million (epm), n - a unit chemical 7.1 Purity o f Reagents-Reagent grade chemicals shall be
equivalent weight of solute pe r million unit weights of solu used in all tests. Unless otherwise indicated, it is intended that
tion. all reagents shall conform to the specifications of the Commit
3.1.2 laboratory control sample, n - a solution with certified tee on Analytical Reagents of the American Chemical Society.5

hardness. Other grades may be used, provided it is first ascertained that

3.1.3 Fo r definitions of other terms used in this test method, the reagent is of sufficiently high purity to permit its use

4 3-Hydroxy-4-( I-hydroxy-2-napththyl) azo-7-nitro-J naphthalenesulfonic

I This test method is under the jurisdiction of ASTM Committee D 19 on Water acid, sodium salt, Color Index 14645.
and is the direct responsibility of Subcommittee D19.05 on Inorganic Constituents 5 Reagent Chemicals, American Chemical Society Specifications, American
in Water. Chemical Society, Washington, DC. For suggestions on the testing of reagents not
Current edition approved 10, 2002. Published June 2002. Originally listed by the American Chemical Society, see Analar Standards fo r Laboratory
published as D1126-50T. Last previous edition D1l26-96. Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
2 Annual Book of ASTM Standards, Vol 11.01. and National FormulGlY, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
3 Annual Book of ASTM Standards, Vol 11.02. MD .

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TABLE 1 Freedom of Reaction from Interfe rences Dissolve 0.2000 g of CaC03 in 3 to 5 mL of HCI (1 + 4). Dilute
Maximum Maximum to 1 L with water.
Concentration Concentration 7.6 Calcium Indicator-Use powdered hydroxynaphthol
Without Without
Substance Interference Interference blue,6 or grind solid hydroxynaphthol blue to 40 to 50 mesh
in the Total in the Calcium size.
Hardness Hardness
7.7 Hardness Indicator-The hardness indicator can be
Test, mg/L Test, mg/L
prepared, stored, and used in liquid or powder form.
Aluminum, A I +  20 5 7.7.1 Hardness Indicator Solution-Dissolve 0.5 g of
Ammonium, NH4 + A
2000 Chrome Black T3 in 50 mL of diethanolamine or triethanola
Bicarbonate, HCOs- 500 mine. Store the solution in a dark-colored bottle. This solution
Bromine, Br 2
Cadmium, C d  20
has a storage life of several months.
Carbonate, COs - 1000 50 7.7.2 Hardness Indicator Powder-Grind 0.5 g of Chrome
Chloride, CI 10000 Black T3 with 100 g of powdered sodium chloride. Use a
Chlorine, CI 2
Chromate, Cr 04 - 500 500
dark-colored bottle for storage. The powder has a storage life
Cobalt, Co++ 0.3 of at least 1 year.
Copper, Cu++ 20 2 7.8 Hydrochloric Acid (1 + 4)-Mix 1 volume of concen
Iron, ferric, F e +  lO B 20
Iron, ferrous, F e  lO B 20 trated hydrochloric acid (sp gr 1.19) with 4 volumes of water.
Lead, Pb++ 20 5 7.9 Disodium Ethylenediamine Tetraacetate (Na2H2 EDTA)
Manganese, Mn++ 1c lO c Solution, Standard (1 mL = 1.0 mg CaC03)-Dissolve 3.8 g of
Nickel, N i - 0.5 D
Nitrate, NO s- 500 500 disodium ethylenediamine tetraacetate dihydrate in approxi
Nitrite, N0 - 500 500 mately 800 mL of water. Adjust the pH of the solution to 10.5
Phosphate,2 P0 4 - - 100 with NaOH solution (50 gIL). Determine the concentration of
Silicate, SiOs - 200 100
Strontium, sr £: £: this solution using the standard calcium solution, and that
Sulfate, S04 - 10000 10000 procedure in Section 9 that will be used for the sample analysis
Sulfite, SOs - - 500 500 (9.1 ,9.2 , or 9.3). Adjust the concentration of the EDTA so that
Tannin, Quebracho 200 50
Tin, stannic, S n - + + 10 5 1 mL will be equivalent to 1.0 mg of CaC0 3. Store the standard
Tin, stannous, Sn++ 10 5 EDTA in polyethylene, plastic, or hard rubber bottles and
Zinc, Z n - 20 5 restandardize monthly.
A No data are available. 7.10 Sodium Hydroxide Solution (50 glL)-Dissolve 50 g of
B Iron will not interfere in concentrations up to 200 mg/L. However, the red color
pOint may return in about 30 s.
sodium hydroxide in water and dilute to 1 L.
c Manganese will not interfere in concentrations up to 10 mg/L if a few crystals
8. Sampling
D Accurate results can be obtained in the presence of 1 mg/L nickel, but the end
ow under these conditions. 8.1 Collect the sample in accordance with Practice D 1066
£: If strontium is present, it will be titrated with calcium and magnesium. or Practices D 3370 as applicable.

9. Procedure
7.2 Purity o f Water-Unless otherwise indicated, reference 9.1 Hardness-Measure 50 mL of clear sample into an
water shall be understood to mean reagent water conforming opaque white container or a clear colorless container utilizing
Specification D 1193, Type 1. Other reagent water types may a white background. Adjust the pH of the sample to 7 to 10 by
is first ascertained that the water is of adding NH40 H solution or HCI solution. Add 0.5 mL of buffer
high purity to permit its use without adversely solution, and approximately 0.2 g of hardness indicator powder
of the test method. Type II or 2 drops of liquid and stir. Add standard Na 2H 2EDTA
specified at the time of round robin testing of this solution slowly from a burette with continuous stirring until the
m e ~ h o d . color changes from red to blue. Complete the titration within 5
7.3 Ammonium Hydroxide Solution (1 + 4 ) - M i x 1 volume min after the buffer addition. I f the titration requires more than
H 4 ~ : ) H (sp gr 0.90) with 4 volumes of water. 20 mL of the titrating solution, dilute the sample and repeat the
7.4 Euffer Solution-Prepare the buffer solution in three test.
as follows: 9.2 Low Hardness-Determine low-hardness values (0.5 to
7.4.1 Dissolve 40 g of sodium tetraborate 5.0 ppm as CaC0 3) in accordance with 9.1, but use a 100 mL
B
2 4 70 ·10H2 0) in 800 mL of water. sample and titrate by means of micro-burette. When employing
7.4.2 Dissolve 10 g of sodium hydroxide (NaOH), 10 g of a 100-mL sample, add twice the quantity of the reagents as
10 g of potassium sodium indicated in 9.1.
0 -4H
4 6 2 0 ) in 100 mL of water. 9.3 Calcium Hardness-Measure 50 mL of the sample into
7.4.3 When cool mix the two solutions and add 1 g of an opaque white container, or a clear colorless container
utilizing a white background. Add 2 mL of NaOH solution and
to 1. Make up to 1 L with

6 3-Hydroxy-4 (2-hydroxy-4 sulfo-l naphthyl) azo-2, 7-naphthalenedisulfonic

7.5 Calcium Solution, Standard (1 mL =0.20 mg CaC03) - acid, trisodium salt.

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cO D 1126
stir. Add approximat ely 0.2 g of calcium indicator and stir. Ad d Calcium hardness, mg/L as CaC0 3 = 1000 D1IS 1 (5)
standard Na2H2EDTA solution slowly from a burette with
where:
continuous stirring until the color changes from red to royal
blue. Complete the titration within 5 min after the NaOH
Dj =
standard Na 2H 2EDTA solution added in titrating
calcium hardness, mL, and
addition. I f the titration requires more than 15 mL of the
S = sample taken, mL.
titrating solution, dilute the sample and repeat the test.
10.2.2 Calculate the magnesium hardness as calcium car

10. Calculations bonate of the sample as follows:

10.1 Calcula te the hardness, epm, of the sample as follows: Magnesium hardness, mg/L as CaC03 = G - H (6)

Hardness, epm = 20 CIS (1) where:

where:
G =
hardness, mg/L as CaC03 , and
H = calcium hardness, mg/L as CaC03 .
epm = equivalent parts per million; milliequivalents pe r
liter, 11. Precision an d Bias 7
C standard Na2H 2EDTA solution added in titrating 11.1 The single operation and overall precision of the total
hardness, mL, and hardness test method within its designated range for 6 labora
S = sample taken, mL. tories, which include a total of 6 operators analyzing each
10.1.1 Calcul ate the calcium hardness, epm, of the sample sample on 3 different days may be expressed as follows:
as follows:
So = 0.0047 X + 0.40
Calcium hardness, epm = 20 DIS (2)
ST = 0.0078 X + 1.80
where:
epm = equivalent parts per million; milliequivalents pe r where:
liter,
So = pooled single-operator precision, mg/L,
S( = overall precision, mg/L, and
D = standard Na2H2EDTA solution added in titrating
X = hardness concentration, mg/L.
calcium hardness, mL, and
11.2 The single operator and overall precision of the cal
S = sample taken for test, mL.
cium hardness test method within its designated range for 6
10.1.2 Calculate the magnesium hardness, epm, of the
laboratories, which include a total of 6 operators analyzing
sample as follows:
each sample on 3 different days may be expressed as follows:
Magnesium hardness, epm = E --: F (3)
So = 0.0052 X + 0.37
where: Sf = 0.D25 X + 0.61
epm = equivalent parts per million; milliequivalents pe r
liter, where:
E hardness, epm, and So = pooled single-operator precision, mg/L
F calcium hardness, epm. S( = overall precision, mg/L, and
10.2 Calculate the hardness as calcium carbonate of the X calci um hardnes s concentration, mg/L.
sample as follows: 11.3 Recoveries of known amounts of hardness and calc ium
hardness in a series of prepared standards for the same
Hardness, mg/L as CaC0 3 = 1000 C/ S 1 (4)
laboratories and operators are as shown in Table 2.
where: 11.4 These data apply to reagent water only. I t is the
C 1 = standard Na2H 2EDTA solution added in titrating analyst's responsibility to ensure the validity of this test
hardness, mL, and method for waters of untested matrices.
S 1 = sample taken, mL. 11.5 Precision and bias for this test method conforms to
10.2.1 Calcu late the calcium hardness as calcium carbonate Practice D 2777 - 77, which Was in place at the time of
of the sample as follows: collaborative testing. Under the allowances made in 1.4 of
D 2777 - 98, these precision and bias data do m eet existing

TABLE 2 Statistic al Information, Total Hardness requirements for interlaboratory studies of Commit tee D 19 test
Amount Amount methods.
Statistically
Added, Found, Bias % Bias
Significant
mg/L mg/L 12. Quality Control (QC)
11.0 11.4 + 0.4 +3.6 No 12.1 The following quality control information is recom
45.0 46.3 + 1.3 + 2.9 No
0.0 No
mended for the determination of hardness in water.
206. 206. 0.0
450. 453. +3 . + 0.7 No 12.2 A check standard shall be analyzed at a minimum
frequency of 10 % throughout the batch analysis. The value of
Calcium Hardness the check standard shall fall between 80 % and 120 % of the
6.2 6.1 -0.1 -1.6 No true value.
25.0 24.9 -0.1 -0.4 No
125. 126. + 1.0 + 0.8 No
250. 250. 0.0 0.0 No 7 Supporting data are available from ASTM International Headquarters. Request
--------.;..----.:..;.:..--------.....:....-- RR: DI9-1125

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• D 1126

12.3 A Laboratory Control Sample shall be analyzed with outside agency in order to determine the laboratory perfor-
of samples at a minimum frequency of 10 %. mance capabilities.
12.4 I f the QC for the sample batch is not within the
13. Keywords
ropriate flags, or bot h (Practice D 5847). 13.1 analysis; calcium carbonate hardness; hardness; titra-
12.5 Blind control samples should be submitted by an tion; water

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