https://www.plotaroute.com/tip/22/how-to-add-labels-and-symbols-to-a-route-map
I would create it on the route, with the direction list and use the water symbol.
The other way is to use the anotate map tool and create an off route point. All anotations can be exported in a gpx and depending in device maybe create a proximity alert for it.
How would I plot a waypoint (for instance a water point) which is slightly off the track?