The Private Water Supplies (Wales) Regulations 2010

Analysing samples

2.—(1) The local authority must ensure that each sample is analysed in accordance with this paragraph.

(2) For each parameter specified in the first column of Table 1 in Part 2 of this Schedule the method of analysis is specified in the second column of that table.

(3) For each parameter specified in the first column of Table 2 in Part 2 of this Schedule the method is one that is capable of—

(a) measuring concentrations and values with the trueness and precision specified in the second and third columns of that table, and

(b) detecting the parameter at the limit of detection specified in the fourth column of that table.

(4) For hydrogen ion, the method of analysis must be capable of measuring a value with a trueness of 0.2 pH unit and a precision of 0.2 pH unit.

(5) The method of analysis used for odour and taste parameters must be capable of measuring values equal to the parametric value with a precision of 1 dilution number at 25°C.

(5) For these purposes—

• “limit of detection” is —

  (a)

  three times the relative within-batch standard deviation of a natural sample containing a low concentration of the parameter; or

  (b)

  five times the relative within-batch standard deviation of a blank sample;

• “precision” (the random error) is twice the standard deviation (within a batch and between batches) of the spread of results about the mean;

• “trueness” (the systematic error) is the difference between the mean value of the large number of repeated measurements and the true value.