I’ve never installed it that way, even in residential settings. I’ve always ran a steel cable and supported each lampholder individually. I certainly wouldn’t run it over a pool without a support cable.
I have those very same lights in my back yard as well. I support them with a messenger cable, each lampholder has a loop at the top which gets ty-rapped to the messenger. You tension the messenger, not the light string. I believe the instructions require it.