How to place a water block in 1.12.9-rc.2

[Gazz]

Found it. It was the cheeky shift key.

[Andrew Clark]

it doesnt work for me it just places the bucket

 

[RapscallionGamer]

I got stuck on this too.  When something like this happens, just set yourself up a little test area, click it, shift click it, control click it, heck, even shift control click that sucker.  At least then you'll hopefully find what you need, and familiarize yourself with some other options too!