Bur seriously though.

The same way they stopped them from cutting themselves and bending the blood that just got out. By severely dehydrating them, and tying them up when fluids were exchanged (like drining, or the occasional pissing). Also, for waterbending to be effective, you need a fair bit of water, and pissing doesn't actually produce a lot of fluids.

Cuss it's a kids show

i never thought about this possibility, amazing

This is that area of the plot that you can kinda-sorta explain but also feel that if it were put to the test it would fail. But if we want to go real-real, then you can find some historical accounts to support some mothods. For example I think the french used to cut the fingers of the english so they couldn't use their longbows anymore. So I think the same would apply here. IF you need your arms to bend, cut it off like Ming-Hua's were. If you are a firebender and need breathing to firebend, jab a fucknig straw into their neck and keep it there with some iron or whatever. They can still get air and not die, but their breathing is fucked. Earthbenders were shown to be carried out to the sea on wooden platforms tho. But obviously it's supposed to be a bit tamer show and not a gorefest so we get less reliable but more friendly methods.

This ia a really excelente question

i´d guess pissbending is easier than bloodbending doe to higher % of actual water but still pretty hard, most benders were not soldiers but just peasants turnt into militia

water bending should be OP since 60% of human body is water. you could literally just control anything in humans and torture them in the worst possible ways

Minimal amount of water need for survival and cuffs for feeding. Did you even watch the show?

cathedars

i think most of them got their arms cut off like Ming-Hua from legend of Korra, most people cant water bend without the arms, and you can still use them to move cargo or pull things.