The fact that it's NOT "cut and dried", is exactly why I suggested he look at his pump specs to see what "his" pump draws...
When the power goes out here, I start my little Honda 2000 inverter gen set... It will run a couple of things at a time, like my fridge, some lights in the house and the fan on my wood stove. OR I can plug in my sump pump and the fans or what ever needs to be run, I just can't run everything all at once.....and I'm OK with that...
For the most important part of all "water", I don't need a generator... I have an artesian well, the water just shoots out of the ground and getting a pail of cold, clean drinking (or what ever else) water is just a pail away,
If I need more water than that, I have a couple nicer "spring fed" ponds,
For an extended power outage, if I want, I can run a trailer mounted PTO genset that I have in the barn. I just pull it up to the house and run it with a small diesel tractor. It easily runs my whole house for showers ect., you can't even tell that you are on generator power...
SR