Akro
The situation in the UK is that one of the things that defines the level of fire cover is the amount of available water/foam. Once an incident requires the use of either of these then the published figure becomes depleted. Because the fire service do not know how much they are going to use during the incident it is not possible to say what the available fire cover is at any time. This assessment can only be made once the incident is over when the Officer in charge will infrom ATC or the Aerodrome Authority of the available cover and when the published level will be restored.
Some large airports will have resources availble which are above and beyond the minimum required for their published cover, and may still be able to operate at their published level. At airports where the fire cover is at a level at or only slightly above the published minimum then once any water or foam is used operations will have to be suspended as you have no idea what cover is or will be available at the end of the incident.