(1) The public water system shall be capable of supplying minimum fire flows either by gravity, or under the following conditions where fire flows are supplied by pumping:

(a) The largest pump out of service at any pumping level,

(b) The highest capacity treatment unit out of service, while maintaining minimum acceptable standards of water quality.

(c) A power outage in effect, unless the appropriate power utility(ies) records indicate a low incidence of electrical outage, defined as follows:

(i) Outages shall average three or less per year based on data for the three previous years with no more than six outages in a single year. Power must be lost for a minimum of thirty minutes in order to qualify as an "outage."

(ii) Outage duration shall average less than four hours based on data for the three previous years. Not more than one outage during the three previous year period shall have exceeded eight hours.

(2) In assessing system reliability, the department shall also give consideration to potential reliability hazards such as reservoir repair or cleaning and/or lack of parallel water transmission lines.