To answer your question, most modern excursion runs are scheduled/designed to not need a water stop en route, unless there are existing facilities (super rare). Modern practice is to subcontract the non-terminal (i.e. not at the yard) water filling out, typically to a local fire service or pool filling company depending on the location and availability. When you look at the economics (money) involved it quickly becomes evident that paying for someone else to fill the tender is cheaper than maintaining facilities to do so. As one gets into more rural communities, the local fire department may be more than willing to undertake these sort of activities as that would be a solid boost to their paltry budget. As water filling infrastructure was normally a "close clearance" point, if it wasn't needed it was eliminated once the railroad could do so; hence my "super rare" comment. Additionally, installing new facilities runs into the same problem of being very close to the track and if done will most likely be on a siding as far out of normal traffic as possible.
I do have some "prototypical" answers about filling steam locomotives both modern excursion and historic regular service. I was involved with a steam program for a while and will emphasize that it ran on the "Keep it Simple"and "6P" (Proper Prior Planning Prevents Poor Performance) methods, and as I alluded to earlier the runs were laid out so that any watering was done at the terminal/yard. The method, believe it or not, was simply a float valve attached to a garden hose left on overnight. At the end of the day the crew simply placed the valve/hose/bracket assembly in the hatch on the tender and turned on the water at the tap. The next morning the crew shut off the water and took out the assembly. This method sported two 16 mile trips, switching, and yard consumption for an average day. With an experienced crew it could support a third trip, however the normal practice was to have the local fire department pump extra water for an extra.
On the same railroad; traditionally, before the demise of steam, there were 4 water stops used. These were used (in this order) as follows: MP 0, MP 21.25, MP 33 (@Jct from connecting RR's water tower) and MP 8. This equates in terms of topography/trip to being; before departure, the other side of "summit" outbound, free water from the other RR, and the other side of the "summit" inbound. I'll try a quick schematic as well. [EDIT] Nope, schematic not working.
Hope this helps.