Apple didn’t go into detail for these metrics, but the screenshot from their Keynote shows basic graphical representations of how each will work.
Water: Your Health app will be able to display how much water you are drinking. This is a metric that will most likely link data from a third party app. For example, when you track your water consumption with a fitness app, that information will automatically link to your native Health app on your iPhone (if you decide to enable that link).
UV exposure: Not sure right now if this will pull data from your location (location based UV information is publicly available), or data from a device that is actually measuring UV index. As I wrote prior, devices that measure UV index are not useful.
Sedentary State: The Apple Watch tracks this feature meticulously, but your iPhone can as well, and I suspect this information will be populated using the Apple M7 and M8 motion processors that started with the iPhone 5S.
Menstruation: Finally Apple adds a feature focused on women. Women will now be able to track their menstrual cycles.