How to Winterize an Outdoor Shower with no Valves
If plumbing supplies an exterior shower that is subject  to freezing weather then any standing water must be drained or it may break the pipes as it freezes. Just shutting the valve off will not remove the water beyond the valve.  Depending on the pipe material, your plumbing skills, and how the piping is configured it would be wise to install valves on the lines that will be subject to freezing weather, but they should be inside if possible. It might be a good idea to also install a "T" connector (also inside) at a low point to the line in order to drain any standing water that would otherwise damage the pipe if frozen. You could attach a hose bib (spigot) to the "T" to make winterizing a simple job. "Ball valves" are best for the shut off valves.