The Public Water Supplies (Scotland) Regulations 2014

[F1 3.   Until 31st December 2019, Scottish Water 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)). S

TABLE 1

Minimum performance characteristic: uncertainty of measurement

Parameter	Uncertainty of measurement (% of prescribed concentration or 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 prescribed concentration or value, except for pH) (Note 2)	Precision (% of prescribed concentration or value, except for pH) (Note 3)	Limit of detection (% of prescribed concentration or 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 prescribed concentration or value for the parameter stated in the table or better. Measurement uncertainty must be estimated at the level of the prescribed concentration or value for the parameter, 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 “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 prescribed concentration or value for the corresponding parameter in Table B.
Note 11: The performance characteristics apply to individual substances, specified at 50 % of the prescribed concentration or value for the corresponding parameter 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”.
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)”.]

Textual Amendments

F1 Sch. 3 substituted (27.10.2017) by The Public Water Supplies (Scotland) Amendment Regulations 2017 (S.S.I. 2017/281), reg. 1(1), sch. 2 (as amended by The Public and Private Water Supplies (Miscellaneous Amendments) (Scotland) Regulations 2017 (S.S.I. 2017/321), regs. 1, 3(3)(a)(b))