"Just drink more water" is offered as skin advice constantly, and it's not wrong exactly, just far less complete than it's usually presented as being.
What Water Intake Actually Does for Skin
Adequate hydration supports overall bodily function, including skin, and severe dehydration can affect skin's appearance and function among many other things in the body. Beyond a baseline adequate intake, though, additional water consumption doesn't meaningfully improve skin hydration the way topical hydration and barrier support do. Skin dryness and body-wide dehydration are related but distinct issues, and drinking water addresses primarily the latter.
Why Topical Care Matters More for Skin Specifically
The skin barrier, not water intake, is what determines how well skin retains the moisture it has, from any source, internal or topical. Someone drinking plenty of water with a compromised barrier can still have visibly dry, flaking skin, because the barrier isn't holding onto moisture regardless of how much is available in the body generally. This is the same barrier-versus-supply distinction that shows up elsewhere in dry skin care: supplying more of something doesn't help if the underlying system can't retain it.
Where the Advice Comes From, and Where It Breaks Down
Adequate hydration genuinely supports skin health as part of overall wellness, which is likely where this advice originated. The breakdown happens when it gets presented as a primary fix for visible dryness, rather than a baseline health factor that matters alongside, not instead of, topical barrier care.
What Actually Helps More
For meaningfully dry or dehydrated-feeling skin, topical hydration, humectants to draw moisture, occlusives to seal it in, and barrier support to enable retention, does more direct work than increasing water intake beyond an already-adequate baseline. Water intake is worth maintaining for overall health. It's not a substitute for addressing what's actually happening at the skin level.