Even if you had that pumping capacity on site, there's no way the municipal water supply could deliver that much water.
You're absolutely right though, if you want big water, that's the way to get it. It's just that "big water" doesn't even begin to approach the scale of the water that would be necessary to directly fight this fire.
SFFD trucks have that capability, and it was used in the 1989 earthquake. It's intended for pulling water from the underground cisterns marked by a big ring of bricks in SF intersections.
Terrible for the equipment to run salt water, but they had to.
My understanding, which is probably quite out of date, is that it's mostly harbor firefighting boats which had this ability.
A coworker of mine points out that many of the San Francisco manholes are actually covers for cisterns of water, which exist primarily for fighting fires after an earthquake possibly takes out the water mains and starts many fires. I should hope that San Francisco fire trucks can draft water to use these.
London Fire Brigade for example has nine special pumps that can draw 2000 gallons a minute each from river or lake supplies. So that's 18,000 gallons a minute just from them.
And that's a smaller fire brigade than Paris.
There were notable logistical issues to get enough firefighters on-site given it’s an island, and there were a ton of people around when the fire broke out. They wound up having 400 firefighters on-site until midnight to get it under control and save the structure. I’m pretty confident they did all they could, and HN’s armchair firefighters aren’t likely to have done any better.
