Turn around time is the key....12 seconds to fill 1600 gallons and an unlimited supply source less than 1, 2 miles away? With a water source that close those two planes are doing much more than people realize.
Not to derail, but when I first saw the news the other day of them being used and with their quick turnaround time, it reminded me of documentary of the Marines fighting on Peleliu during WW2.
Marine Corsair pilots had most likely the shortest flight bombing runs of the war. After ground troops took the runway, Marine pilots supporting the ground troops upon taking off from the runway, and dropping their bombs just off the departure end of the airfield where Japanese troops were embedded on the cliffs overlooking the airfield and mortaring Marines. Take off, drop bombs over departure end, turn back downwind, land, re-arm, and repeat.
Have him look at these...won't break the bank and will do what is needed. Have him focus on the GPM, so with these at least a 2" discharge. Don't forget at least a 100' discharge line (and nozzle).
https://www.harborfreight.com/search?q=water pump