Confirmed. You can't even refill second bottle, only way is to drop filled one, refill second one, then get one from floor.

You can refill the second one, just empty your hands and drag the empty one into your hands in the inventory screen.

your inventory reads like a book from left to right when your refilling said water bottle or canteen with water fill one open inv and move your empty water bottle or canteen to where the full one is or to the left of it then close back and then pick your bottle up and fill it

I understand how it is working in game. I'm saying, I shouldn't have to open my inventory. I should be able to click on the tool bar and expect the specific item i placed there to be selected. Players when this game is live will expect that functionality.

Confirmed, even if its working somehow it´s still bugged.

Yes. The hotbar only recognizes one inventory item of each type. I have noticed it with other items. The inventory bar seems to select only the first item of that type in inventory. Even if you want to have two programmed so you can control your inventory a little better, still, the slot is associated with the first item of that type. I think I even noticed this when the item had been placed on teh floor. The item was showing in the VICINITY box. I had put it down, but because it was within reach, it was showing as available in the inventory bar. I will try to look at this again next time I play and report back...

ive also experienced this issue while trying to fill one of two canteens, never could equip the empty canteen in ui bar

Hello TITAN and thank you for the report.
This is an issue we are aware of (#0022419) and it has been scheduled for a fix.
Regards,
Geez