The role of fluid balance
The kidneys play a fundamental role in regulating fluids. When they do not function properly, the body can retain fluid. This usually causes swelling, not more visible veins.
In fact:
Swollen hands can make veins appear less visible.
Dehydration, on the other hand, can make veins look more prominent.
Mild dehydration reduces plasma volume, causing veins to become temporarily noticeable. While severe or repeated dehydration can overload the kidneys, the presence of visible veins alone does not indicate kidney damage.