Hello and thanks for the reply.
I've taken 3 open water swims since posting, and I followed all the instructions in the user guide on every swim. Only the 2nd swim's water temperature was recorded in the Health app.
A couple things to note: My "When Submerged" Auto-Launch App is set to the Depth app, but it never launches automatically. I always have to launch the Depth app manually. I also manually launch an Open Water Swim workout just as I get in the water.
During the 1st swim, I only launched the Depth app once mid-swim to view the water temp, but the temp was not recorded in the Health app, and the Apple Watch was still not set a Data Source for Water Temperature.
During the 2nd swim, I launched the Depth app several times, including at the end of the swim. The water temp was recorded in the Health app, and the Apple Watch was finally set as a Data Source for Water Temperature! At this point, I thought I was good.
However during the 3rd swim, I launched the Depth app a couple times to view the water temp, but again the water temp was not recorded in the Health app.
Any ideas what is going on -- and why its so hard to record water temp in the Health app?