Hot water agents flow from an invisible spring in the center of the world, at a rate set by a slider. They slowly evaporate as they wiggle, and die if their size drops to almost zero or they reach the edge of the world. A widget creates other springs in the same area.
The water agents have a 1/1000 chance of creating a mineral deposit, and if they do, they become smaller. If a water agent collides with an existing deposit, it has a 1/50 chance of creating another deposit nearby.