How would I add a Thirst requirement and bar

Maybe with an overlay that has display conditions based on a variable. 

Like, create 10 overlays for each level of thirst and set their display conditions depending on the variable. 

you prb will need a Global Var (Player Lifetime) - this will save when u leave the world and reset when the player dies, then:

• make a procedure (OnPlayerTickUpdate) - to timer your thrist decays and also to modify the value here when player drink water, make a Return of that variable on the end of the procedure

• make a procedure to Return the current value (from the last procedure) of the Variable (thrist) so u can display on the Overlay

  let me know if u made it work, i made a bank acount system like that (mine is player persistent thou, so wont reset on player death) but the rest its the same i think, i might be able to help you more :)

and no you dont need 10 overlays, all u need is to Return the Current value of the Thrist variable on the overlay, work with my variable so should work for you :)

for your thirst bar u need to make 10 images (1 display on each condition - bar 25%, 50% and so on, so u need 10 bars over each other on the Same overlay), like condition 1 -> if Return value (current thrist) = max value (full bar) /  5 = 20% so this will display the bar at 20% for example, i also made this for fuel and energy bars so principle is the same, but instead of Return current energy you return the current thrist (global var)

clarifying - 10 images for bars that go 10% for condition

5 images - 20% per conditions and so on

Yes, 10 images, not 10 overlays, thanks for the correction. 

You can make tick counter timer for this.

https://www.youtube.com/watch?v=gTbWiMu-M-0

https://www.youtube.com/results?search_query=mcreator+tick+timer

Try on player tick update. 

You can save anyway, this is warning only:

On world tick update global trigger is tick event based. Keep in mind that running to complex or demanding procedures each tick can impact game performance

yeah its a warning so people know if they start to put A LOT of stuff on world/player ticks off course the game might lag (fps drop) - btw u should use OnPlayerTickUpdate (since its a player variable) instead of OnWorldTickUpdate, less heavy