Ah, we have some of those highly-chlorinated foot washers like this one but only because you have to pass through them to reach the swimming pools.
But those are usually not mapped here, as they are not an amenity (something you would seek) themselves (instead, swimming pool is what you seek). Now other examples at the link you shared seem like they would be an actual amenity=*, with similar purpose like that air blower, but just for cleaning footwear (or bare foot?) with water (instead of compressed air)?
I tend to agree with @alan_gr above that it probably would be best to suggest each of them as a separate amenity=* tag.
I would advise against that. Single proposal suggesting multiple tags is much more likely to fail (as people who like 90% of proposal but dislike 10% would still vote “no”). So it is much better to do several separate proposals, even it is a little more work, there is much higher chance they (or majority of them) would pass.
That of course can be done, but I think going via proposal process is much better, as other people will give feedback and result in better tag (and its description) overall. Here there is currently only 3 of us discussing, at is is already with more ideas and better way than if it was just one person. With proposal process, final suggestion will get even better than the 3 of us can come up with.
As you note, trying to change the way something is already being mapped is going to create waaaaay more friction and thus problems then if you just proposed how to map things that are currently having no tag at all (which should go smoothly in cases like this). So I’d just go with new propositions (one proposition for each tag to be added).
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