> The body is considered to be adequately hydrated when the body fluids lost through sweating, urination, or respiration have been replaced and when the levels of water in the body are sufficient to maintain the proper functioning of organs and systems.
Years ago, on my gout website, I realized the importance of adequate hydration. Because for gout sufferers, poor hydration increases the concentration of uric acid. Which is a Very Bad Thing!
During my first decade of gout, I used to think there was a target for daily fluid intake. But as you say, the amount of water we need to drink or eat depends on many, changing factors.
Later, I learned that the best approach is to consider urine colour. Which should be the colour of pale straw. I.e., not completely clear. As that might indicate over hydration that might harm the kidneys.
Source: Mentes, Janet. "Oral hydration in older adults: greater awareness is needed in preventing, recognizing, and treating dehydration." AJN The American Journal of Nursing 106, no. 6 (2006): 40-49.
> Urine that is the color of pale straw usually indicates a normal hydration status; as urine darkens, poorer hydration may be indicated (after the effect of discoloration by food or medications has been ruled out).