[Chummy]

Would this involve having 75 gallon water heater tanks, etc. for each individual room? How does one safeguard the common areas, eg, dining halls, hallways, restrooms, support facilities for the building?

[Old Professer]

Indeed, it is one such unit for each room; the hallways and the rest are generally low-risk ignition areas and not necessarily protected in many buildings.

Actually, I started with the idea of using a bladder-fitted tank with the bladder enclosed inside the tank and chargeable from an outside source with air at normal ASME air tank pressures of 120-200PSI but this would require a special construction and would cost more but would be far simpler.

In any case, I figure the device would need to dump (rain) at least one inch of water in less than 5 minutes to be effective, which is why I said it would take at least 63 gallons for a 10 foot by 10 foot floor area.