# The Water Intended for Human Consumption (Private Supplies) (Scotland) Regulations 2017, Paragraph 3

Extent: S

Until 31st December 2019, the enforcing authority may, for a parameter in Table 2, use the corresponding ‘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
Aluminium
25
Ammonium
40
Antimony
40
Arsenic
30
Benzo(a)pyrene
50
Note 5
Benzene
40
Boron
25
Bromate
40
Cadmium
25
Chloride
15
Chromium
30
Conductivity
20
Copper
25
Cyanide
30
Note 6
1,2-dichloroethane
40
Fluoride
20
Hydrogen ion concentration (in pH)
0.2
Note 7
Iron
30
Lead
25
Manganese
30
Mercury
30
Nickel
25
Nitrate
15
Nitrite
20
Oxidisability
50
Note 8
Pesticides
30
Note 9
Polycyclic aromatic hydrocarbons
50
Note 10
Selenium
40
Sodium
15
Sulphate
15
Tetrachloroethene
30
Note 11
Trichloroethene
40
Note 11
Trihalomethanes: total
40
Note 10
Total organic carbon
30
Note 12
Turbidity
30
Note 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
Aluminium
10
10
10
Ammonium
10
10
10
Antimony
25
25
25
Arsenic
10
10
10
Benzo(a)pyrene
25
25
25
Benzene
25
25
25
Boron
10
10
10
Bromate
25
25
25
Cadmium
10
10
10
Chloride
10
10
10
Chromium
10
10
10
Conductivity
10
10
10
Copper
10
10
10
Cyanide
10
10
10
Note 6
1,2-dichloroethane
25
25
10
Fluoride
10
10
10
Hydrogen ion concentration (in pH)
0.2
0.2
Note 7
Iron
10
10
10
Lead
10
10
10
Manganese
10
10
10
Mercury
20
10
20
Nickel
10
10
10
Nitrate
10
10
10
Nitrite
10
10
10
Oxidisability
25
25
10
Note 8
Pesticides
25
25
25
Note 9
Polycyclic aromatic hydrocarbons
25
25
25
Note 10
Selenium
10
10
10
Sodium
10
10
10
Sulphate
10
10
10
Tetrachloroethene
25
25
10
Note 11
Trichloroethene
25
25
10
Note 11
Trihalomethanes: total
25
25
10
Note 10
Turbidity
25
25
25
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”.
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)”.
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”.

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Source: https://www.legislation.gov.uk/ssi/2017/282/schedule/4/paragraph/3 (the official version)
Page: https://openlegislation.uk/water-intended-for-human-consumption-private-supplies-scotland-regulations-2017/schedule-4/paragraph-3
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.