Recently we have begun testing out pump cans. I like them better than water extinguishers because you can refill them on scene. I would support carrying only them and removing the water extinguisher altogether. We also carry dry chem and foam extinguishers on all first out engines.
I thought he meant back-pack sprayers. We use them a lot for grass fires. They work very good. We don't carry water extinguishers on our pumper. We've got the dry chemical and foam extinguishers and 4 backpacks. Put 4 guys in the grass/bush with them and they can put out a fire in a hurry. I'd have to double check, but I would guess that they hold about 4 gallons of water. No pressurization like a weed sprayer, just a pump-action wand.
We also carry the "native american cans," but this is a replacement for the water extinguisher as pictured below. Some might call them a hand pump extinguisher. We are using the 2.5 Gal to comply with 1901
All or Engine Companys cary back pack pumps for grass fires, and a pressurized water extinguisher. Our Ladder trucks cary a pressurized water extinguisher and a pump style like what Mike Batt pictured above.
All trucks cary the dry chem as required, and the engines also carry a Class D extinguisher.