Likelihood	Description	rate
Frequent	Is expected to occur in most circumstances (more than one time per a year), has been observed regularly in the field, confirmed by water quality	5
Most probable	Will probably occur in most circumstances (at least one time per a year), has been observed occasionally in the field, confirmed by water quality	4
Probable	Might occur at some times (once per two years), has been observed occasionally in the field, no significant water quality data trend that confirm the risk	3
Improbable	Could occur at some time (once per 5 years), has not been observed in the field, no water quality data trends that confirm the risk	2
Infrequent	May occur only in exceptional circumstances (didn’t happened during 5 years), has not been observed in the field, water quality data do not indicate any risk	1
Severity	Description	rate
Negligible	Negligible impact on water quality, service delivery or normal operation	1
Slight	Minor water quality influence for slight fraction of users, certain practicable description to process, corrective action required for service delivery, rise in complaints not significant	2
Sensible	Minor water quality influence for huge fraction of users, clear growth in objections, public displeasure, slight gap of monitoring requirement, regulator interest, significant but manageable modification to normal operation, increased operational cost, increase monitoring	3
considerable	Major water quality impact for small percentage of customers, large numbers of complaints, and significant breach of regulatory requirement, regulator interest and investigation, system is significantly compromised with abnormal operation, extra high level of monitoring required	4
Terrible	Major water quality impact for large percentage of users, disease in public related with the water system, litigation by customers, major regulatory breach, major investigation by regulator with prosecution likely, complete failure of system	5