This is a popular one, perpetuated by fitness and fashion magazines.
Only one study ever linked drinking water with skin hydration. That study used expensive mineral water, not plain bottled or tap water, and the study didn’t have a control group.
No study has ever shown regular water has any impact on your skin and no controlled study has ever shown that any type of drinking water has an effect on your skin.
From a physiologic perspective, drinking water could only have a negligible impact on your skin’s hydration. In fact, patients who have too much water in their tissues (edema) do not have healthy skin. For example, patients with venus insufficiency who have swollen, fluid filled legs have skin that is often dry, itchy, and scaly.
The amount of water in your skin after a 5 minute shower is magnitudes higher than you could achieve by trying to hydrate it from the inside out. The key is to apply a cream or ointment when your skin is still wet to seal in the moisture.
Then drink as little or as much water as you like.