I suspect what he means is “anywhere” on water, not just parking spots in water runway airports or addon water runway airports.
Shameless plug, but you can actually start anywhere on water (or land) with Location Manager for MSFS - Sonicviz (pro version) [disclosure: developer of LM]
It’s a little bit of a process via creating the saved location from the main map (or fly mode) then in Fly mode you can select the saved location and teleport to an engine stopped state on ground/water or engine on (duh!) flying in air @ 1000ft iirc. Then you can begin whatever flight startup process you wish. You can currently save 200 locations, & I may increase this in future.
The reason for the process is multiple. There’s an issue that custom waypoints selected on the main map always have a set height of 1640ft/500m, which makes getting the altitude for ground/water a little tricky, when it should be able to just pop it in there on the map. Also, it appears custom waypoint starts are always in the air at a height depending on the aircraft type, and there was no way I could see to hook into that to do a custom ground/water start anyway. There is no flexibility there, by design.
I asked this on the dev forum:
Q: Why don’t custom waypoints have correct altitude?
POI’s, runways, airports etc all have correct altitude set in the location object in world locationinfos, but custom waypoints altitude are fixed at 1640ft or 500m everywhere.
I’m on SU12 beta, but I think this is also the case in live.
A:
Yoanito answered • Mar 14 2023 at 6:10 PM BEST ANSWERACCEPTED ANSWER
Hello @sonicviz
This altitude value is hard coded because waypoints in general have no altitude, the POI altitude is right because it has been set by hand.
It is made like this by design and won’t be changed.
Best regards,
Yohan
Ah, but waypoints in general DO have altitude, if you want them to. For whatever reason(s), they decided it wasn’t needed.
So I found a way to do it in Location Manager anyway so you can get set up anywhere on ground/water, but if MSAsobo do actually look into doing this properly from the main map akin to the current starting location process they will encounter the same issues that will need to be resolved first.