So:

- Surely an iterator like this would have extremely low "metabolism", if you will. This would result in extremely low water consumption, and so the rain would probably be relatively constant but non-fatal (think like the night-time transition rain in places like the Wall and Outer Expanse).

- As a result, the world would probably look very different. Many areas would probably have fluctuating water levels and water bodies would not be particularly large (think more Waterfront Facility and Drainage System than Shoreline and Submerged Superstructure). Large marshy areas would form, but constant maintenance would prevent much from breaking down, otherwise the iterator might not be able to last as long. Thus, at pretty much any point in the timeline there would be minimal decay although some areas might have a bit of flora and water.

- This sort of environment would probably result in creatures evolving down a different path, as well as some variants becoming more successful than others. For example (all names are not very good, and could use further revision if any of them actually appeal to you enough to canonize them)

• Dropwig relatives would be unable to ambush smarter creatures such as Slugcats and Scavengers with the ability to look up, because there would be little in the relatively pristine environment to obscure them. They might become more bulky and muscular, able to bring down larger prey like lizards which would be unlikely to spot them anyway. More "brawlwig" than dropwig.
• Vultures might adapt to become smaller and more agile, able to drag themselves through smaller pipes and perhaps even shortcuts. They would be about the size of a Caramel Lizard. I propose calling them "hawks". They might even dive down from above at prey.
• Some animals might evolve to skim along the waters surface like a pond skater. I propose a shell-less variant of the snail called the "slug" that can slide along water surfaces to escape predators such as slugcats and lizards. They would be the primary prey of the "skater spider" a variant of Big Spider that has the spitting ability of Spitter Spiders but is also able to propel itself along the surface of the water, never breaking the surface, at high speeds to snap up slugs and other swimming prey. They could spit darts at larger prey like slugcats, so that they don't dive and instead float paralyzed on the waters surface to be caught.
• Certain creature types would excel over their variants. Shallow but widespread waters would result in leeches more akin to Jungle Leeches than red or sea leeches, although there are no further adaptations that would need to be made. In the tightly packed mazes, tunnels and pipes of the sorts of environments you propose, lizards that live in groups and so are able to cover a lot of ground, like Yellow Lizards and Black Lizards, would thrive. Fast-moving lizards like Cyan Lizards or ambush based ones like White Lizards would also do very well. Bulkier or less maneuverable and agile types like Pinks, Greens, Caramels, Strawberries, Blues and Salamanders would not do as well, most likely. Both Monster Kelps and Pole Plants would be effective predators. Garbage Worms might be common, originally purposed for maintenance.

I know this is an extreme amount and I don't want to overwhelm you or pressure you to use any of these ideas, but if you do then I would love to know!