There is a sticky on the top of the page which explains that.
Many, many people fail to read it and post exactly this sentence. As one of them, what would you do so that people find this sticky?
Concerning your issue. A minion is not dead till there is a “death processing phase reached”. Both actions (Vargoth & Waterbearer) are end of turn effects. They happen in the end of turn phase. Death is checked after the phase only.
Check this if you want to understand Hearthstone game mechanics better:
https://hearthstone.gamepedia.com/Advanced_rulebook#Death_Phases_and_consequences_of_Death