ASTM D1126-17

Standard Test Method for Hardness in Water

SIGNIFICANCE AND USE
5.1 Hardness salts in water, notably calcium and magnesium, are the primary cause of tube and pipe scaling, which frequently causes failures and loss of process efficiency due to clogging or loss of heat transfer, or both.  
5.2 Hardness is caused by any polyvalent cations, but those other than Ca and Mg are seldom present in more than trace amounts. The term hardness was originally applied to water in which it was hard to wash; it referred to the soap-wasting properties of water. With most normal alkaline water, these soap-wasting properties are directly related to the calcium and magnesium content.
SCOPE
1.1 This test method covers the determination of hardness in water by titration. This test method is applicable to waters that are clear in appearance and free of chemicals that will complex calcium or magnesium. The lower detection limit of this test method is approximately 2 to 5 mg/L as CaCO3; the upper limit can be extended to all concentrations by sample dilution. It is possible to differentiate between hardness due to calcium ions and that due to magnesium ions by this test method.  
1.2 This test method was tested on reagent water only. It is the user's responsibility to ensure the validity of the test method for waters of untested matrices.  
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 30-Nov-2017
• ICS: 13.060.50 - Examination of water for chemical substances
• Technical Committee: D19 - Water
• Drafting Committee: D19.05 - Inorganic Constituents in Water

Relations

• Refers: ASTM D1066-18 - Standard Practice for Sampling Steam
• Effective Date: 01-Aug-2018
• Refers: ASTM D1066-18e1 - Standard Practice for Sampling Steam
• Effective Date: 01-Aug-2018

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D1126 − 17
Standard Test Method for
1
Hardness in Water
This standard is issued under the fixed designation D1126; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope* D2777 Practice for Determination of Precision and Bias of
Applicable Test Methods of Committee D19 on Water
1.1 Thistestmethodcoversthedeterminationofhardnessin
D3370 Practices for Sampling Water from Closed Conduits
water by titration. This test method is applicable to waters that
D5847 Practice for Writing Quality Control Specifications
are clear in appearance and free of chemicals that will complex
for Standard Test Methods for Water Analysis
calcium or magnesium. The lower detection limit of this test
methodisapproximately2to5mg/LasCaCO ;theupperlimit
3
3. Terminology
can be extended to all concentrations by sample dilution. It is
possible to differentiate between hardness due to calcium ions
3.1 Definitions:
and that due to magnesium ions by this test method.
3.1.1 For definitions of terms used in this standard, refer to
Terminology D1129.
1.2 This test method was tested on reagent water only. It is
the user’s responsibility to ensure the validity of the test
3.2 Definitions of Terms Specific to This Standard:
method for waters of untested matrices.
3.2.1 equivalent per million (epm), n—a unit chemical
1.3 The values stated in SI units are to be regarded as equivalent weight of solute per million unit weights of solu-
standard. No other units of measurement are included in this tion.
standard.
3.2.2 laboratory control sample (LCS), n—a solution with
1.4 This standard does not purport to address all of the
certified hardness.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
4. Summary of Test Method
priate safety, health, and environmental practices and deter-
4.1 Calcium and magnesium ions in water are sequestered
mine the applicability of regulatory limitations prior to use.
by the addition of disodium ethylenediamine tetraacetate. The
1.5 This international standard was developed in accor-
endpointofthereactionisdetectedbymeansofChromeBlack
dance with internationally recognized principles on standard-
3
T , which has a red color in the presence of calcium and
ization established in the Decision on Principles for the
magnesium and a blue color when they are sequestered.
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
5. Significance and Use
Barriers to Trade (TBT) Committee.
5.1 Hardness salts in water, notably calcium and
2. Referenced Documents
magnesium, are the primary cause of tube and pipe scaling,
2
which frequently causes failures and loss of process efficiency
2.1 ASTM Standards:
D1066 Practice for Sampling Steam due to clogging or loss of heat transfer, or both.
D1129 Terminology Relating to Water
5.2 Hardness is caused by any polyvalent cations, but those
D1193 Specification for Reagent Water
other than Ca and Mg are seldom present in more than trace
amounts. The term hardness was originally applied to water in
1
which it was hard to wash; it referred to the soap-wasting
This test method is under the jurisdiction of ASTM Committee D19 on Water
and is the direct responsibility of Subcommittee D19.05 on Inorganic Constituents
properties of water. With most normal alkaline water, these
in Water.
soap-wasting properties are directly related to the calcium and
Current edition approved Dec. 1, 2017. Published December 2017. Originally
magnesium content.
approved in 1950. Last previous edition approved in 2012 as D1126 – 12. DOI:
10.1520/D1126-17.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
3
Standards volume information, refer to the standard’s Document Summary page on 3–Hydroxy–4-(1–hydroxy-2–napththyl) azo-7–nitro–1 naphthalenesulfonic
the ASTM website. acid, sodium salt, Color Index 14645.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1

---------------------- Page: 1 ----------------------
D1126 − 17
TABLE 1 Freedom of Reaction from Interferences
7.2 Purity of Water—Unless otherwise indic
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D1126 − 12 D1126 − 17
Standard Test Method for
1
Hardness in Water
This standard is issued under the fixed designation D1126; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope*
1.1 This test method covers the determination of hardness in water by titration. This test method is applicable to waters that are
clear in appearance and free of chemicals that will complex calcium or magnesium. The lower detection limit of this test method
is approximately 2 to 5 mg/L as CaCO ; the upper limit can be extended to all concentrations by sample dilution. It is possible
3
to differentiate between hardness due to calcium ions and that due to magnesium ions by this test method.
1.2 This test method was tested on reagent water only. It is the user’s responsibility to ensure the validity of the test method
for waters of untested matrices.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2
2.1 ASTM Standards:
D1066 Practice for Sampling Steam
D1129 Terminology Relating to Water
D1193 Specification for Reagent Water
D2777 Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water
D3370 Practices for Sampling Water from Closed Conduits
D5847 Practice for Writing Quality Control Specifications for Standard Test Methods for Water Analysis
3. Terminology
3.1 Definitions—For definitions of terms used in this test method, refer to Terminology D1129.
3.1 Definitions:
3.1.1 For definitions of terms used in this standard, refer to Terminology D1129.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 equivalent per million (epm), n—a unit chemical equivalent weight of solute per million unit weights of solution.
3.2.2 laboratory control sample (LCS), n—a solution with certified hardness.
4. Summary of Test Method
4.1 Calcium and magnesium ions in water are sequestered by the addition of disodium ethylenediamine tetraacetate. The end
3
point of the reaction is detected by means of Chrome Black T , which has a red color in the presence of calcium and magnesium
and a blue color when they are sequestered.
1
This test method is under the jurisdiction of ASTM Committee D19 on Water and is the direct responsibility of Subcommittee D19.05 on Inorganic Constituents in Water.
Current edition approved March 1, 2012Dec. 1, 2017. Published March 2012December 2017. Originally approved in 1950. Last previous edition approved in 20072012
ε1
as D1126 – 02 (2007)D1126 – 12. . DOI: 10.1520/D1126-12.10.1520/D1126-17.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
3
3–Hydroxy–4-(1–hydroxy-2–napththyl) azo-7–nitro–1 naphthalenesulfonic acid, sodium salt, Color Index 14645.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1

---------------------- Page: 1 ----------------------
D1126 − 17
TABLE 1 Freedom of Reaction from Interferences
Maximum Maximum
Concentration Concentration
Without Without
Substance Interference Interference
in the Total in the Calcium
Hardness Hardness
Test, mg/L Test, mg/L
+ + +
Aluminum, Al 20 5
+ A
Ammonium, NH 2 000
4
−
Bicarbonate, HCO . 500
3
Bromine, Br . 2
+ +
Cadmium, Cd 20 .
− −
Carbonate, CO 1 000 50
3
−
Chloride, Cl 10 000 .
Chlorine,
...