I think people tune this out though because it often feels like overkill for the season/weather or something else. Obviously the weather changes or the exposure is different once you're out there. But it won't stop people tuning it out. The signposted hike in question is very, very tame, maybe 1.5km.

I like the per-trail signage idea. Broader things like 4L/day recommendations aren't going to seem realistic for many people. Or education around over-provisioning water: added weight makes for more exercise, and means you're not miserly rationing water and hating the hike.