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The Water Intended for Human Consumption (Private Supplies) (Scotland) Regulations 2017

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PART BChemical and indicator parameters

1.—(1) Subject to paragraph 3, for a parameter in Table 1, the method of analysis used must, as a minimum, be capable of measuring concentrations equal to the parametric value for the parameter with—

(a)a limit of quantification of 30 % or less of the parametric value; and

(b)an uncertainty of measurement as specified in Table 1.

(2) The result of the analysis for a parameter in Table B or Table C must be expressed using at least the same number of significant figures as the parametric value for the parameter in the table.

2.  The uncertainty of measurement specified in Table 1 must not be used as an additional tolerance to the parametric values.

3.  Until 31st December 2019, the enforcing authority may, for a parameter in Table 2, use the correponding ‘trueness’, ‘precision’ and ‘limit of detection’ in that table as an alternative set of performance characteristics (instead of using the limit of quantification and the uncertainty of measurement referred to in paragraph 1(1)).

TABLE 1

Minimum performance characteristic: uncertainty of measurement

Parameter

Uncertainty of measurement

(% of parametric value, except pH) (Note 1)

Notes(1)
Aluminium25
Ammonium40
Antimony40
Arsenic30
Benzo(a)pyrene50Note 5
Benzene40
Boron25
Bromate40
Cadmium25
Chloride15
Chromium30
Conductivity20
Copper25
Cyanide30Note 6
1,2-dichloroethane40
Fluoride20
Hydrogen ion concentration (in pH)0.2Note 7
Iron30
Lead25
Manganese30
Mercury30
Nickel25
Nitrate15
Nitrite20
Oxidisability50Note 8
Pesticides30Note 9
Polycyclic aromatic hydrocarbons30Note 10
Selenium40
Sodium15
Sulphate15
Tetrachloroethene30Note 11
Trichloroethene40Note 11
Trihalomethanes: total40Note 10
Total organic carbon30Note 12
Turbidity30Note 13

TABLE 2

Minimum performance characteristics: trueness, precision and limit of detection

Parameter

Trueness

(% of parametric value, except for pH) (Note 2)

Precision

(% of parametric value, except for pH) (Note 3)

Limit of detection

(% of parametric value, except for pH) (Note 4)

Notes(2)
Aluminium101010
Ammonium101010
Antimony252525
Arsenic101010
Benzo(a)pyrene252525
Benzene252525
Boron101010
Bromate252525
Cadmium101010
Chloride101010
Chromium101010
Conductivity101010
Copper101010
Cyanide101010Note 6
1,2-dichloroethane252510
Fluoride101010
Hydrogen ion concentration (in pH)0.20.2Note 7
Iron101010
Lead101010
Manganese101010
Mercury201020
Nickel101010
Nitrate101010
Nitrite101010
Oxidisability252525Note 8
Pesticides252525Note 9
Polycyclic aromatic hydrocarbons252525Note 10
Selenium101010
Sodium101010
Sulphate101010
Tetrachloroethene252510Note 11
Trichloroethene252510Note 11
Trihalomethanes: total252510Note 10
Turbidity252525

Notes to Table 1 and Table 2

Note 1: Uncertainty of measurement is a non-negative parameter characterising the dispersion of the quantity values being attributed to a measurand, based on the information used. The performance criterion for measurement uncertainty (k = 2) is the percentage of the parametric value stated in the table or better. Measurement uncertainty must be estimated at the level of the parametric value, unless otherwise specified.

Note 2: Trueness is a measure of systematic error, i.e. the difference between the mean value of the large number of repeated measurements and the true value. Further specifications are those set out in international standard ISO 5725 entitled “Accuracy (trueness and precision) of measurement methods and results”(3).

Note 3: Precision is a measure of random error and is usually expressed as the standard deviation (within and between batches) of the spread of results from the mean. Acceptable precision is twice the relative standard deviation. This term is further specified in international standard ISO 5725 entitled partly “Accuracy (trueness and precision) of measurement methods and results”.

Note 4: Limit of detection is either three times the standard deviation within a batch of a natural sample containing a low concentration of the parameter, or five times the standard deviation of a blank sample (within a batch).

Note 5: If the value of uncertainty of measurement cannot be met, the best available technique should be selected (up to 60 %).

Note 6: The method determines total cyanide in all forms.

Note 7: Values for trueness, precision and uncertainty of measurement are expressed in pH units.

Note 8: Reference method European standard EN ISO 8467:1995 entitled “Water quality - Determination of permanganate index (ISO 8467:1993)”(4).

Note 9: The performance characteristics for individual pesticides are given as an indication. Values for the uncertainty of measurement as low as 30 % can be achieved for several pesticides, higher values up to 80 % may be allowed for a number of pesticides.

Note 10: The performance characteristics apply to individual substances, specified at 25 % of the parametric value in Table B.

Note 11: The performance characteristics apply to individual substances, specified at 50 % of the parametric value in Table B.

Note 12: The uncertainty of measurement should be estimated at the level of 3 mg/l of the total organic carbon in accordance with European standard EN 1484:1997 entitled “Water analysis - Guidelines for the determination of total organic carbon and dissolved organic carbon”(5).

Note 13: The uncertainty of measurement must be estimated at the level of 1.0 nephelometric turbidity units in accordance with European standard EN ISO 7027-1:2016 entitled “Water quality - Determination of turbidity - Part 1: Quantitative methods (ISO 7027-1:2016)”(6).

(1)

Acrylamide, epichlorohydrin and vinyl chloride to be controlled by product specification.

(2)

Acrylamide, epichlorohydrin and vinyl chloride to be controlled by product specification.

(3)

This standard has been approved by the International Organization for Standardization (ISO). Under reference BS ISO 5725-1 to BS ISO 5725-6, these are published as UK standards by the British Standards Institution.

(4)

This standard was approved by the European Committee for Standardization (CEN) on 3rd November 1994. Under reference EN ISO 8467:1995, it is published as a UK standard by the British Standards Institution (ISBN 0 580 23435 5).

(5)

This standard was approved by the European Committee for Standardization (CEN) on 6th April 1997. Under reference BS EN 1484:1997, it is published as a UK standard by the British Standards Institution (ISBN 0 580 28372 0).

(6)

This standard was approved by the European Committee for Standardization (CEN) on 15th April 2016. Under reference BS EN ISO 7027-1:2016, it is published as a UK standard by the British Standards Institution (ISBN 978 0 580 81961 2).

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