maybe Dr. Lisa can weigh in....?
I actually have a master's degree and a PhD in (human) nutrition. Not that I know anything

, but to let you know that my thought is an informed one...
The way the digestive system works is that it breaks things down that are consumed. So any bad things are theoretically weeded out before they are absorbed into the body. (Sent to the liver to be detoxified.) So it's safer to eat something, than to inject it, in theory. The fact that subcut fluids are injected is a testament to the fact that they are pure/clean/ok for the body without the filtering of the digestive system.
If something like a drug in injected in the body, bypassing this system, it's to get past all the enzymes that break things down (why insulin is injected not taking orally--it doesn't work), or to get it to needed cells more quickly--straight into the blood stream.
All that is in this solution is water and electrolytes---similar to found in Gatorade (only no sugar!) So my sense is that this is purified water with electrolytes and so might be fine, even a good thing to give. I give distilled water which is also 'purified'. Although perhaps the sodium is not a good idea for the kidney disease--although it sort of depends because not sure how much is in there and also it's in there with other balancing electrolytes so may not be the same issue as giving a high-sodium food.
Anyway, OF COURSE, I'm going to donate these if I don't use them.
But if it would be good for Fred to have these as a pure and helpful water source--then I would like to use them.
By the way, I just bought the Drinkwell fountain for Fred, hoping he's going to drink more. He's never had this before but seems to really like it so far. I put the distilled water in there.
I wonder if Dr Lisa could weigh in on this...?