Groundwater Movement (Interactive)
has.concord.orgIf you want to try out a more topical model try this:
Very nice, but doesn't model pressure.
It also models pumps in a pretty exaggerated way. Two pumps will prevent this basin from ever filling up despite constant rainfall, to the point of creating a concave water surface: https://imgur.com/a/PrYFJtP
You can gain a lot of intuition for system behavior via particle models like this and their many, many other interactives.
I also recommend looking at their library of learning resources that put these interactives into context: https://learn.concord.org/collections
Cool interactive, also +1 for being from my hometown
I worked there until 10 years ago and it was quite rewarding. (In fact this interactive uses some of the "lab" framework code I worked on.)
The founder was inspired by Concord (Massachusetts)'s history of progressive educational experimentation, going back to the transcendentalists (Emerson, Thoreau).
They're based in Concord but they also have a Bay Area office, after merging with the nonprofit org that built CODAP (https://codap.concord.org/)