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Appendix 2: Tables A1.3 and A1.4 from the DWSNZ

Table A1.3: Allowable exceedances (for 95% confidence that the MAV is exceeded for no more than 5% of the time)

Exceedances

Number of samples

0

38–76

1

77–108

2

109–138

3

139–166

4

167–193

5

194–220

6

221–246

7

247–272

8

273–298

9

299–323

10

324–348

Table A1.4: Allowable exceedances (for 95% confidence that the MAV is exceeded for no more than 2% of the time)

Exceedances

Number of samples

0

95–193

1

194–274

2

275–349

3

350–420

4

421–489

5

490–556

6

557–621

7

622–686

8

687–750

9

751–813

10

814–875

The following may assist in interpretation of these tables. It is based on Table A1.3 which is appropriate for E. coli monitoring.

For a supply to comply with respect to E. coli, E. coli must not be detected (ie, there must be fewer than one organism per 100 ml) in any sample if the total number of samples taken is no more than 76. If the number of samples taken is between 77 and 108 then E. coli may be detected in one sample. If the sample number is between 109 and 138 two samples may be positive for E. coli, and so on. Clearly, one positive sample is also acceptable if more than 108 samples have been taken.