Drinking Water Ordinance as of 2023

The current Drinking Water Ordinance (as of March 2023) provides the following calculation examples for the approaches 2 x 0.5 ml and 1x 50 ml:

| Case studies for the number of evaluable target colonies | Indication on test report [CFU/100 ml] | Conformity assessment |
|--|--|--|
| Case A: No legionella detected on all plates (DA + MF) | < 2 | TMW not reached |
| Case B: Σ DA without detection, MF 1-2 CFU | < 6 | TMW not reached |
| Case C: Σ DA 1-2 CFU, MF 0-2 CFU | < 100 | TMW not reached |
| Case D: Σ DA 0-2 CFU, MF 3 - 49 | 6 - 98 | TMW not reached |
| Case E: Σ DA 0-2 CFU, MF 50 - 80 | 100 - 160 | TMW reached |
| Case F: Σ DA 3 - 600 CFU, MF not relevant for overall assessment | 300 - 60,000 | TMW reached |
| Case G: Σ DA > 600 CFU, MF not relevant for overall assessment | > 60,000 | TMW reached |
| Case H: Σ DA 1-2 CFU or not evaluable, MF > 80 CFU | > 160 | TMW reached |

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Example Parameters

Below is an example of calculating legionella according to the current (as of March 2023) Drinking Water Ordinance.
For this, 3 parameters are created, one for direct approaches, one for membrane filtration, and one that calculates the final result.

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Configuration Parameter Legionella Direct Approach
For the 1st parameter for the two 0.5 ml approaches, 6 columns are created in this example, which are configured as follows:

| Column | Column Label | Data Type | Purpose |
|--|--|--|--|
| 0 | CFU/100ml | blocked | Here, the CFU/100 ml from Plate 1 and 2 are calculated, manual inputs are blocked |
| 1 | Companion Flora | -,+,++,+++ | Selection of the strength of the companion flora |
| 2 | Confirmed Colonies Plate 1 | /^na$\|^na\\\*$\|^> *300$\|^([0-9]\|[1-9][0-9]\|[1-3][0-9][0-9]\|300)$\|^$/ | Indication of confirmed colonies on Plate 1, possible inputs limited to na, na\*, 0-300, >300 by data type |
| 3 | Confirmed Colonies Plate 2 | /^na$\|^na\\\*$\|^> *300$\|^([0-9]\|[1-9][0-9]\|[1-3][0-9][0-9]\|300)$\|^$/ | Indication of confirmed colonies on Plate 2, possible inputs limited to na, na\*, 0-300, >300 by data type |
| 4 | Suspicious Colonies Plate 1 | | Indication of suspicious colonies on Plate 1 |
| 5 | Suspicious Colonies Plate 2 | | Indication of suspicious colonies on Plate 2 |

In column 0, a formula is entered which calculates the concentration per 100 ml from the confirmed colonies of Plate 1 and 2 from columns 2 and 3. For this purpose, the ifs formula goes through every combination of possible inputs for Plate 1 and 2 and decides what should happen:

| Formula Part | Purpose |
|--|--|
| ifs( | **open ifs formula** |
|istzahl(this(2))&&istzahl(this(3)),(this(2)+this(3))*100, | **if both results are numbers -> add both numbers and multiply by 100** |
| this(2)==='na'&&this(3)==='na','na', | **if both plates are not evaluable -> output 'na'** |
| this(2)==='na'&&this(3)==='na*','na*', | **Plate 1 not evaluable, Plate 2 not evaluable, but legionella found -> output 'na\*'** |
| this(2)==='na*'&&this(3)==='na','na*', | **Plate 2 not evaluable, Plate 1 not evaluable, but legionella found -> output 'na\*'** |
| this(2)==='na*'&&this(3)==='na*','na*', | **both plates not evaluable, but legionella found -> output 'na\*'** |
| istzahl(this(2))&&this(2)==0&&this(3)==='na*','0*', | **Plate 1 has 0 colonies, Plate 2 not evaluable, but legionella found -> output '0\*'** |
| istzahl(this(3))&&this(3)==0&&this(2)==='na*','0*', | **Plate 2 has 0 colonies, Plate 1 not evaluable, but legionella found -> output '0\*'** |
| (this(2)==='na'\|\|this(2)==='na*'\|\|contains(this(2),'>'))&&istzahl(this(3)), 200*this(3), | **Plate 1 not evaluable or >300, Plate 2 had colonies -> multiply Plate 2 by 200** |
| (this(3)==='na'\|\|this(3)==='na*'\|\|contains(this(3),'>'))&&istzahl(this(2)), 200*this(2), | **Plate 2 not evaluable or >300, Plate 1 had colonies -> multiply Plate 1 by 200** |
| '> 60000' | **both plates >300 -> output '> 60000'** |
| ) | **close ifs formula** |

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Legionella Membrane Filtration Configuration Parameters

For the 2nd parameter, the 50 ml approach, 4 columns are set up in this example, as follows:

| Column | Column Label | Data Type | Purpose |
|--|--|--|--|
|0| CFU/100ml | blocked | Here, the CFU/100 ml is calculated from the confirmed colonies, manual inputs are blocked |
|1| Accompanying Flora | -,+,++,+++ | Selection of the strength of accompanying flora |
|2| Confirmed Colonies | /^$\|^na$\|^na\\\*$\|^> *80$\|^([0-9]\|[1-7][0-9]\|80)$/ | Specification of confirmed colonies, possible inputs restricted by data type to na, na\*, 0-80, >80 |
|3| Suspect Colonies | | Specification of suspect colonies |

A formula is placed in Column 0, which calculates the concentration per 100 ml from the confirmed colonies in Column 2:


| Formula Component | Purpose |
|--|--|
| ifs( | **open if formula** |
|istzahl(this(2)),this(2)*2, | **if the result is a number -> multiply by 2** |
| contains(this(2),'>'), '> 160', | **if the result is greater than 80 -> output '> 160'** |
| this(2) | **otherwise output result (na, na\*)** |
| ) | **close if formula** |

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Legionella Final Result Configuration Parameters
For the 3rd parameter for the final result calculation, 3 columns are set up in this example, as follows:

In Column 0, a formula is placed, which calculates the concentration per 100 ml from direct inoculation and membrane filtration:


| Formula Component | Purpose |
|--|--|
| ifs( | **open if formula** |
|m['Leg_D']['0']>200 \|\| m['Leg_D']['0']==='> 60000', m['Leg_D']['0'], | **if the result of direct inoculation > 200 -> output direct inoculation result** |
|m['Leg_MF']['0']>4 \|\| m['Leg_MF']['0']==='> 160', m['Leg_MF']['0'], | **if the result of membrane filtration > 4 -> output membrane filtration result** |
|m['Leg_D']['0']==='na'&&m['Leg_MF']['0']==='na','na', | **if both results are not evaluable -> output 'na'** |
|m['Leg_D']['0']==='na'&&m['Leg_MF']['0']==='na*','na*', | **if both results are not evaluable, but Legionella were found in membrane filtration -> output 'na\*'** |
|m['Leg_D']['0']==='na*'&&m['Leg_MF']['0']==='na','na*', | **if both results are not evaluable, but Legionella were found in direct inoculation -> output 'na\*'** |
|m['Leg_D']['0']==='na*'&&m['Leg_MF']['0']==='na*','na*', | **if both results are not evaluable, but Legionella were found in both -> output 'na\*'** |
|istzahl(m['Leg_D']['0'])&&m['Leg_D']['0']==0&&m['Leg_MF']['0']==='na','< 100', | **if no Legionella were found in direct inoculation and membrane filtration is not evaluable -> output < 100** |
|istzahl(m['Leg_MF']['0'])&&m['Leg_MF']['0']==0&&m['Leg_D']['0']==='na', '< 2', | **if no Legionella were found in membrane filtration and direct inoculation is not evaluable -> output < 2** |
|istzahl(m['Leg_MF']['0'])&&m['Leg_MF']['0']==0&&istzahl(m['Leg_D']['0'])&&m['Leg_D']['0']==0, '< 2', | **if no Legionella were found in both -> output <2** |
|istzahl(m['Leg_MF']['0'])&&m['Leg_MF']['0']==0&&m['Leg_D']['0']==='na*', '< 2*', | **if no Legionella were found in membrane filtration and direct inoculation is not evaluable, but Legionella were found -> output < 2\*** |
|istzahl(m['Leg_MF']['0'])&&m['Leg_MF']['0']==0&&m['Leg_D']['0']==='0*', '< 2*', | **if no Legionella were found in membrane filtration and one plate was without Legionella in direct inoculation, but not evaluable, and the other with Legionella -> output < 2\*** |
|m['Leg_D']['0']==='na'&&istzahl(m['Leg_MF']['0']), '< 6*', | **if Legionella were found up to 2 in membrane filtration and direct inoculation is not evaluable -> output < 6\*** |
|m['Leg_D']['0']==='na*'&&istzahl(m['Leg_MF']['0']), '< 6*', | **if Legionella were found up to 2 in membrane filtration and direct inoculation is not evaluable, but Legionella were found -> output < 6\*** |
|m['Leg_D']['0']==='0*'&&istzahl(m['Leg_MF']['0']), '< 6*', | **if Legionella were found up to 2 in membrane filtration and one plate was without Legionella in direct inoculation, but not evaluable, and the other with Legionella -> output < 6\*** |
|istzahl(m['Leg_D']['0'])&&m['Leg_D']['0']==0&&istzahl(m['Leg_MF']['0']), '< 6*', | **if Legionella were found up to 2 in membrane filtration and no Legionella were found in direct inoculation-> output < 6\*** |
|'< 100*' | **in all other cases (Legionella were found up to 2 in direct inoculation) -> output <100\*** |
| ) | **close if formula** |



In Column 1, a formula is placed, which selects the relevant accompanying flora from direct inoculation and membrane filtration:
| Formula Component | Purpose |
|--|--|
| ifs( | **open if formula** |
|m['Leg_D']['0']>200 \|\| m['Leg_D']['0']==='> 60000', m['Leg_D']['1'], | **if the result of direct inoculation > 200 -> output accompanying flora of direct inoculation** |
|m['Leg_MF']['0']>4 \|\| m['Leg_MF']['0']==='> 160', m['Leg_MF']['1'], | **if the result of membrane filtration > 4 -> output accompanying flora of membrane filtration** |
|m['Leg_Endresult']['0']==='na' \|\| m['Leg_Endresult']['0']==='na*','-', | **if the final result is na or na\* -> output a -** |
|m['Leg_Endresult']['0']==='< 2'\|\|m['Leg_Endresult']['0']==='< 2*'\|\|m['Leg_Endresult']['0']==='< 6*',m['Leg_MF']['1'], | **if the final result is < 2, <2\* or < 6\* -> output accompanying flora of membrane filtration** |
|m['Leg_D']['1'] | **otherwise output accompanying flora of direct inoculation** |
| ) | **close if formula** |



In Column 2, a formula is placed, which selects the relevant approach from direct inoculation and membrane filtration:

| Formula Component | Purpose |
|--|--|
| ifs( | **open if formula** |
|m['Leg_D']['0']>200 \|\| m['Leg_D']['0']==='> 60000', 'DA', | **if the result of direct inoculation > 200 -> output DA** |
|m['Leg_MF']['0']>4 \|\| m['Leg_MF']['0']==='> 160', 'MF', | **if the result of membrane filtration > 4 -> output MF** |
|m['Leg_Endresult']['0']==='na' \|\| m['Leg_Endresult']['0']==='na*','-', | **if the final result is na or na\* -> output a -** |
|m['Leg_Endresult']['0']==='< 2' \|\| m['Leg_Endresult']['0']==='< 2*' \|\| m['Leg_Endresult']['0']==='< 6*','MF', | **if the final result is < 2, <2\* or < 6\* -> output MF** |
|'DA' | **otherwise output DA** |
| ) | **close if formula** |