Rule clarifications
These tables help to clarify some of the interpretations in the Drinking Water Quality Assurance Rules.
The Drinking Water Quality Assurance Rules were published on 25 July 2022. When we next update the Rules, we will include any required amendments and clarify interpretations in the guidance we are developing.
Treatment Rules for all levels
Rule / Requirement |
Rule / Requirement description |
Rule / Requirement clarification |
Treatment Rules for drinking water treatment plants with recycled waste streams are listed below: T3.29, T3.33, T3.37 and Table 24 (pages 49, 50) T3.41, T3.45, T3.49 and Table 25 (pages 51, 52) T3.62 and Table 27 (pages 54, 55) T3.79 and Table 29 (pages 57, 58) |
Drinking water treatment plants with recycled waste streams have process limitations outlined in section 4.10.2 T3 Protozoal Rules.
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Additional clarification for treatment plants with recycle streams:
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UV Validation Requirements T1.7 (pages 25 and 26) T2.11 (page 31) T3.20 and Table 22 (pages 45, 46) T3.91 and Table 32 (pages 61-63) |
All references to DVGW Technical Standard W294 (DVGW 2006) and ÖNORM M 5873-1:2020-01-01 |
The transition of DVGW Technical Standard W294 to DIN 19294. A new DIN 19294-1:2020-08 Standard has been released to replace DVGW Technical Standard W294-2. The DIN 19294-1:2020-08 and ÖNORM M 5873-1:2020-01-01 are identical in content, therefore where ÖNORM M5873-1:2020-01-01 is referenced the DIN 19294-1:2020-08 will also be accepted as a suitable UV validation/certification standard. All rules and requirements applicable to ÖNORM M5873-1:2020-01-01 apply to DIN 19294-1:2020-08. |
Level 1 Rules
Rule / Requirement |
Rule / Requirement description |
Rule / Requirement clarification |
T1.8 (page 26)
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Water leaving the treatment plant must be monitored for the determinands and at the frequencies set out in Table 10. |
The current stated compliance periods in T1.8 and Table 10 are 6 months which is inconsistent with other references. The compliance periods in Table 10 should be 3 months to be consistent with G1 and Table 3. |
Level 2 Rules
Rule / Requirement |
Rule / Requirement description |
Rule / Requirement clarification |
T2.1 and Table 14 (pages 30, 33) Rule D2.1 and Table 15 (pages 34, 35)
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T2 Treated water monitoring and D2 Distribution system monitoring have requirements for: Duration between samples |
The duration between samples is the period that must elapse before a supplier can take the next sample. Example for Tables 14 and 15: If a supplier samples on Monday and must meet a requirement for an ‘At least 2 Days’ duration between samples, another sample must be taken on Wednesday or thereafter. The supplier must still meet the sampling frequency requirement. These requirements should not be interpreted as limiting the amount of sampling done in a week. A supplier may take more samples than the sampling frequency, but at least two of those samples need to be taken within the specified duration between samples. |
G2 and Table 4 (pages 17, 20) |
Reporting requirements for Level 2 Supplies are shown in Table 4. |
Additional clarification on the reporting requirements in Table 4: The referenced rule numbers and parameters are inconsistent in some places. Table 4 is shown below with the correct references to rules and parameters highlighted in yellow. |

Rules for supplies with Varying Population
Rule / Requirement |
Rule / Requirement description |
Rule / Requirement clarification |
VP.3 and Tables 41 and 42 (pages 80, 81)
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VP Increased monitoring for treatment plants and distribution zones have requirements for: Duration between samples |
The duration between samples means the duration must elapse before a supplier can take the next sample for compliance purposes. Example for Tables 41 and 42: If a supplier takes a sample on Monday and the sampling frequency is daily with a duration between samples of 12 hours, they are required to take another sample on Tuesday. These requirements should not be interpreted as limiting the number of samples taken in a day. |
Level 3 Source Water Rules
Rule / Requirement |
Rule / Requirement description |
Rule / Requirement clarification |
Source Water Protozoa Log Credit Treatment Requirements (page 36) |
Class 2 – Protozoa Barrier – 3 log Criteria: Groundwater sources that draw water from a depth of between 30 metres and 10 metres below ground level (with depth measured from ground level to the top of the uppermost screen). |
Criteria clarification: Groundwater sources that:
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Source Water Protozoa Log Credit Treatment Requirements (page 37)
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Class 3 - Protozoa Barrier – 4 log Criteria: Groundwater sources that draw water from a depth of less than 10 metres below ground level (with depth measured from ground level to the top of the uppermost screen), groundwater sources that draw water from a depth of 10 or more metres below ground level without a sanitary bore head, spring water sources and surface water sources. |
Criteria clarification: Groundwater sources that draw water from a depth of 10 metres or less below ground level (with depth measured from ground level to the top of the uppermost screen), spring water sources and surface water sources.
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Level 3 Treatment Rules
Rule / Requirement |
Rule / Requirement description |
Rule / Requirement clarification |
T3 Rules with requirements to meet a parameter for a percentage of a day (e.g., T3.2, T3.5, T3.8, T3.10, T3.13, T3.16, T3.24, T3.27, T3.31, T3.35, T3.39, T3.43, T3.47, T3.51, T3.60, T3.65, T3.81, T3.85, T3.86, T3.89) |
Section 3.1 (page 14) states: Drinking water suppliers only need to demonstrate compliance against the Rules for periods when a drinking water supply is operating. Example: Rule T3.5 (page 41). The turbidity of water leaving the treatment plant must be less than 1 NTU for at least 95% of each day. |
Additional clarification for requirements to meet a parameter for a percentage of a day when a treatment plant or process does not operate for all of a day: A treatment plant or process “is operating” when it is producing drinking water to be distributed to consumers. Example: Rule T3.5 should be interpreted as: The turbidity of water leaving the treatment plant must be less than 1 NTU for at least 95% of the time the treatment plant is producing drinking water to be distributed to consumers. |
T3.15 and Table 22 (pages 45, 46) |
UVT monitoring under T3 Bacterial Rules requires: UVT is to be monitored for water entering or leaving the UV reactor(s). |
The requirements of section 4.10.1.4 Table 22 are the same as the requirements of 4.10.2.13 Table 32 (footnote 56) (page 62): The requirement to monitor UVT does not apply to UV disinfection systems that automatically adjust the UV dose as the UVT of the water flowing through the reactor varies. The UV disinfection system may still require monitoring of UVT to meet the manufacturers’ validation criteria and requirements. |
T3.79 and Table 29 (pages 57, 58) |
Membrane filtration process limitations under T3 Protozoa Rules require: If flows of greater than 10% are recycled, the separate treatment of the recycled waste stream is required to inactivate or kill protozoa and bacteria before the waste stream is returned to the drinking water treatment plant upstream of the membranes. |
Inactivating or killing protozoa includes processes that remove protozoa. |
T3.93 and Table 33 (pages 65, 66) |
Section 4.10.3 (page 64) states: If sodium hypochlorite is used, chlorate must be monitored weekly, regardless of the levels determined by sampling. |
Additional clarification for Section 4.10.3: If sodium hypochlorite is used, sampling of chlorate must be weekly as per Table 33 unless footnote 62 (page 66) is met. |
Level 3 Distribution System Rules
Rule / Requirement |
Rule / Requirement description |
Rule / Requirement clarification |
D3.20 and Table 35 (pages 71, 73) Rule D3.29 and Table 39 (pages 75, 76) |
FAC and microbiological sampling under D3 Distribution System Rules have requirements for: The maximum interval between samples. |
The maximum interval between samples (days) means a supplier must take the next sample before the maximum interval has elapsed. Example: If the supplier samples on Monday at 10 am and must meet a requirement for a 2-day maximum interval between samples, then another sample must be taken before the end of Wednesday. |
D3.20 and Table 35 (pages 71, 73) D3.29 and Table 39 (pages 75, 76) |
FAC and microbiological sampling under D3 Distribution System Rules have requirements for: The minimum number of days of the week used. e.g., For >100,000 zone population, the Minimum number of days of the week used is 7 (at least four Saturdays and four Sundays sampled each year) |
The minimum number of days of the week used is assessed over the course of the year and reported on in the annual report by a supplier and is not required to be met for each monthly compliance period. It refers to the spread of sampling days in a week, i.e. weekdays and weekends, to ensure the sample represents a spread of days and trends. |