Instead of huge drone carrying water (we already have planes to do that now), I was envision a network of connected drones that "pass by" the water as they hover in the line all the way from water pool to fireplace. The video attached previously shows you group of drones perfectly communicating with each other.
I never said it was easy to develop, but I have to disagree its something "way beyound the current levels" of technology. Further, the cost to design, develop and implement would be pennies comparing to an average damage of mid-size fire. Not the mention about life-loss.