A single infinite CLEAN water tile only found in forests.
Boiled by the earth’s magma deep in the core, and pushed up through a vent in the crust into a nice neat little water sprout.
Actually being from New England springs are not that uncommon. Also there is a lot of small streamlets and what not. I have no idea how hard it would be to create something to cause these (small streams and brooks) to be added to the math on non-specific tiles. There is a brook behind the house I grew up in that doesn’t go above you knees except in a few rare spots. It’s rocky as heck, as streams and rivers tend to be in New Hampshire.
I like the idea.
I live in New England. I have a well which only passes through a sediment filter. I also have a spring down by the brook behind the house.