The cost would be a trifle compared to the potential losses. Running at 5 gal/min a 10,000 gallon swimming pool would last a day and a half, maybe more. Crazy idea, maybe, but I’d give it a try.

Generator/electric pump/impact sprinkler sounds good as long as the gen has a big fuel tank, otherwise someone needs to be there to refuel and make sure the pump reprimes if it conks out. Also, when the adjacent property faces your place with a 100' high wall of flames blowing your way at 50-100mph, it's like spitting in the wind; your sprinkler water goes downwind... not in the direction of the oncoming flames.

I had an uncle in Mandeville canyon (on Rivers Road if you care to look at the terrain on Google maps satellite imaging). Like many homeowners in the red tagged canyons, my uncle had an average sized pool and a standard Briggs 2" pump in the pool shed. I ran it during a fire in the 1980s. We have similar pumps on all our salvage boats so it was second nature to me to run the thing except for the climbing up and down the ladder to refuel the thing every 45 mins so it doesn't starve and lose prime. When the smoke got sketchy in the canyon we left because if you don't get out early, that Mandeville Rd becomes impassable. His house dodged the bullet without me on the roof. Rain that spring filled his pool with mud.

A well known surfer I grew up surfing with in SoCal, George Trafton, tried to save his house up by Topanga Canyon with a garden hose on Tuesday. He's in an ICU now. I have a hunch a lot of bodies will be found that were trying to defend with hoses or pool&pumps.