ASTM D1126 - 12

    Standard Test Method for Hardness in Water

    Active Standard ASTM D1126 | Developed by Subcommittee: D19.05

    Book of Standards Volume: 11.01


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    ASTM D1126

    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.

    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 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 and health practices and determine the applicability of regulatory limitations prior to use.


    2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.

    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


    ICS Code

    ICS Number Code 13.060.50 (Examination of water for chemical substances)

    UNSPSC Code

    UNSPSC Code


    DOI: 10.1520/D1126

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