Summary

This is probably too esoteric a need to be useful to most people, but if you spend a lot of time in an infinity pool then you'll know the frustration of wanting to stand near the edge of the pool since that's generally got the best view / vibe, only to realize that there's nowhere to put your drink/phone/speaker, because there's nothing to stop a mild splash or wave from sending them off the side of the building.
Having to hold your stuff above the water or walk to the other side of the pool every time you want to adjust the music or have a drink is a compromise that people who aren't willing to spend a couple dozen hours over-engineering a cupholder have to make.

If your infinity pool happens to have an edge that's <56mm wide, then you don't have to compromise either.

Because there's no good way to clamp down to the side of a pool edge that has water actively flowing over it, and there's no easy way to measure the angle and curve of the back side of the drainage wall, I've made several design choices to mitigate the risk of water carrying this over the edge. The center of gravity should be roughly over the center of the pool wall, and the flat portion of the shelf has flow holes to allow water to pass through the part instead of lifting it off the wall. On the back side there are a set of 5 holes sized for an M5 bolt to cut its own thread, so that bolts can be inserted to act as spacers to correct the distance/angle on an inconsistently sloped drainage wall. These knobs are designed to make hand adjustment of the bolts easier https://www.thingiverse.com/thing:6170124

The Cupholder platform is effectively sitting on stilts to allow water to flow underneath it and out of the pool. This elevation also serves to keep electronics above the water, and prevent the flow of water from transferring heat to the beverage. For similar reasons, the side of the cupholder facing the water is solid to prevent water ingress, but because some amount of splashing is inevitable, there are egress channels on the drainage side to allow any water that enters to flow out instead of pooling inside the cupholder. Both cupholders have a 95mm inner diameter, so they should fit most large insulated water bottles, cell phones, or small-medium bluetooth speakers

Either part could be used independently, but they're designed to be printed separately and then bolted together with M5 bolts, both to allow for easier printing via different slicer settings/orientation, and so that the base can be swapped out if there's fitment issues with the pool edge.