I would advise you talk to Craig Harrison about F9. He'll be able to tell you what kind of pump and nozzle you'll need. Personally I wouldn't carry any kind of acid on my back. Never know what could happen and thats not something you want to be messing with.
And just FYI; the back pack wfp idea came from the UK in order to conserve water as they did windows. It's also one of the reasons why they have smaller WFP hoses as well, to conserve water. That's not something you need to be worried about and carrying a backpack full of DI water isn't something that's needed. I know RHG and many others have the pure water systems on trolleys that can just be towed around. Very easy and less of backache. As for demos a pump up sprayer would work just fine for demos.