IWA Publishing

Table 1

The descriptive information on risk level (Petts 2009)

Level	Descriptor	Description
1	Insignificant	No detectable, or insignificant health impact. No disruption to normal operation. Insignificant impact to normal operating costs.
2	Minor	Short term or localized aesthetic non-compliance, not related (e.g. Fe, Mn, H₂S, Zn, color, odor, taste, turbidity). Manageable disruption. Minor impact on normal operating costs.
3	Moderate	Widespread aesthetic issues or long-term non-compliance, not health related (for instance Fe, Mn, H₂S, Zn, color, odor, taste, turbidity). Significant impact to normal operation but manageable. Significant impact to normal operating costs.
4	Major	Potential long-term health effects or chronic toxicity (for example chemical organic constituents; for instance pesticides, trihalomethanes (THMs), or inorganic constituents including Hg, Cd, Pb). System significantly compromised; high level of monitoring is required. Disruption to consumers in the supply.
5	Catastrophic	Potential illness or acute toxicity (for instance microbial, chemical organic constituents; for example pesticide, or inorganic constituents; for example CN). Major impact for large population. Complete system failure.

Level	Descriptor	Description
1	Insignificant	No detectable, or insignificant health impact. No disruption to normal operation. Insignificant impact to normal operating costs.
2	Minor	Short term or localized aesthetic non-compliance, not related (e.g. Fe, Mn, H₂S, Zn, color, odor, taste, turbidity). Manageable disruption. Minor impact on normal operating costs.
3	Moderate	Widespread aesthetic issues or long-term non-compliance, not health related (for instance Fe, Mn, H₂S, Zn, color, odor, taste, turbidity). Significant impact to normal operation but manageable. Significant impact to normal operating costs.
4	Major	Potential long-term health effects or chronic toxicity (for example chemical organic constituents; for instance pesticides, trihalomethanes (THMs), or inorganic constituents including Hg, Cd, Pb). System significantly compromised; high level of monitoring is required. Disruption to consumers in the supply.
5	Catastrophic	Potential illness or acute toxicity (for instance microbial, chemical organic constituents; for example pesticide, or inorganic constituents; for example CN). Major impact for large population. Complete system failure.