If the player's cup touches the trigger part, the water comes out the spout and goes in the cup.
script.Parent.Touched:Connect(function(hit)
if hit.Parent.Name == "Tool" then
workspace.Water.Transparency = 0
game.StarterPack.Tool.Handle.InCup.Transparency = 0
end
end)

4 comments
You wont see changes made to the tool because the server does not have the startertools constantly updating whatever is in someone's backpack. When someone joins, all those starterpack tools get cloned to them. You'll need to change the one in backpack, or if it's equipped, the one in their character
So how would I clone it to the character? Because it needs to be equipped for the trigger part to work.
maybe hit.Parent:IsA("Tool")?
I'll try that..