A3.10 Calculation of LRVs using the QMRA framework

Table A3.7 outlines the assumptions that are used in the QMRA process and establishing consumption volumes of unheated water at 1L per day. Using the health impact data in Table A3.6, together with the reference pathogen concentrations in Table A3.4, the LRVs were calculated for each category. The calculated LRVs by treatment category are summarised in Table A3.8.

Table A3.7 Model assumptions applied in the QMRA

Model assumption	Reference pathogen	Reference pathogen	Reference pathogen
	Cryptosporidium	Virus	Campylobacter
Dose-response parameter (r)(Exponential)⁽¹⁾	0.2	0.69	0.019
Probability of illness given infection (Pill inf)⁽²⁾	0.7	0.7	0.3
DALY per 1000 cases⁽³⁾	1.7	0.57	23.5

Notes:

1. Taken from Table A3.5 and is the same as the probability of infection per organism. In other words, it is estimated that 20% of cryptosporidium oocysts will cause illness.

2. Taken from Table A3.5. It is estimated that 70% of cryptosporidium infections lead to illness.

3. Taken from Table A3.6.

Source specific data for reference pathogens may be used where data is available (see Chapter 5 Box 5.7). This should be done in consultation with the relevant health authority or drinking water regulator.

Table A3.8 Calculated LRVs by source water category (based on concentrations for respective pathogens as outlined in Table A3.4)

Source water category	Maximum or 95ᵗʰ percentile⁽¹⁾ E. coli results from raw water monitoring (number/100 mL)	LRV⁽²⁾ based on Indicative average Cryptosporidium concentration (oocysts/L)	LRV⁽²⁾ based on estimated Adenovirus concentration (MPNIU/L)	LRV⁽²⁾ based on Campylobacter concentration (MPN/L)
Category 1	<20 (WHO E. coli Band 1)	0.0	< 3.2	< 2.8
Category 2	20 to 2000 (WHO E. coli Band 2)⁽³⁾	2.9 – 3.9	3.2 – 4.2	2.8 – 3.8
Category 3	20 to 2000 (WHO E. coli Band 2)⁽³⁾	3.9 – 4.9	4.2 – 5.2	3.8 – 4.8
Category 4	>2000 to 20,000 (WHO E. coli Band 3)	4.9 – 5.9	5.2 – 6.2	4.8 – 5.8

Notes:

1. Maximum E. coli results from raw water representative of inlet to treatment plant should be used unless data set is robust enough to use 95ᵗʰ percentile

2. LRV = Log ((concentration of reference pathogens in source water/L x $P _{inf}$ x $P_{ill/inf}$ x DALY per case x 365)/($10^{-6}$)) Where $P_{inf}$ = dose response, $P_{ill/inf}$= probability of illness given infection (see Table A3.7) and 365 = consumption of drinking water per year (L).

3. Maximum E. coli results for raw water monitoring for source water Categories 2 and 3 are within the same range and distinguishing between these two categories is confirmed based on the results of the vulnerability classification.

Abbreviations: MPN most probable number; MPNIU most probable number infectious units.