It's not bad for a first game with RPG Maker.

Here are a few things that you need to fix :

• The tile that I bordered in red (in all cells) makes the player able to walk on top of the walls.

Potential spoiler.

• The events that you created here are underneath the player which means he needs to step into the poisoned water before triggering them using a button. 

And as a player :

1. If I think that I should pick up water, I'll try to pick it up from the side of the pool, not inside it.
2. If picking up the water from the border doesn't work, I might try stepping inside the pool, but if it turns out that it damages me, the first thing I'll think about is getting out of there, I won't bother trying to pick up water.

To be honest I wanted to suicide by walking inside the pool, and I randomly clicked on the same tile I was in, which triggered the event and made me continue the game, so I suggest you make the event at the same level as the player and tick the "Through" option so that he can pick up water from the side, but also get damaged if he tries to step in it. Or you can find your own way to do things.

• And then there's a few small things like the battle balance, the "Run" option that has 100% chance of success, and the chest that changes its image when you interact with it after it has already been opened (tick the "Direction Fix" option after it has been opened), but these things become natural as you have more and more experience with the engine.

Overall, it was not bad, better that my first game with RPG Maker lol. And I really hope you'll keep developping the game. Now that the jam is over, you'll have more freedom to use scripts, different tilesets, and resources other than the base ones.