Of course they need water! Its really important for them, like for every creature on earth. :-)
And it's especially important for this species because they do not eat any honey or sugarwater. Other species additionally get water from those food sources.
So you must give them water with cottonwool? Or just pure water without cottonwool? And wat about a nest in a testtube with water behind cottonsool in the tube, do you still have to give them water outside the nest in this situation?
You HAVE to give them water. If you dont want them go swimming you can use the cotton. I prefer giving them water without.
I would give them some honey, too. Perhaps they need it. You cant say that they do not need honey becoause they do not drink any or because anything else.
I don't give mine any honey or sugar mix. They just don't like it. I do give them plenty of fresh water is a bird feeder, with cotton to prefent them from drowning.