I use an app called WaterMinder (it’s free, with a tipping option) that’s available for iPhone and Apple Watch. Whenever I drink some water (or water containing

I use an app called WaterMinder (it’s free, with a tipping option) that’s available for iPhone and Apple Watch. Whenever I drink some water (or water containing beverage), I just tap the app complication on the watch face and the appropriate water intake icon. You can configure different buttons/water volumes for a single-tap ease of use. Or you can tap on “Other” and then choose the kind of beverage and volume. The app also has some adjustments on hydration percentages for different beverages (for example, if you drink black coffee, it will take 90% of the volume as water intake). You can even edit those values if you wish. I track only the water I consume in beverages (including plain water), and don’t try to estimate the water contained in solid or cooked foods.