Unfortunately, the moisture in your skin is usually not related to dehydration and drinking a lot of water every day is unlikely to be beneficial. In truth, we really don't know why some people have very moist skin and others do not. If you are someone who has particularly dry skin, then you should probably get into the habit of using topical moisturizers on a regular basis. This is especially true if your symptoms are worse in the winter, when dry skin can really be a problem. This will help keep your skin as moist as you want it. Drinking more water will just make your kidneys work overtime getting rid of any excess fluids you drink. Your body will not deliver that extra fluid to your skin.
I think that you would be best served to schedule an appointment with your primary care physician
. This type of thing be evaluated by your doctor
just to make sure your skin has no other issues. You may even get a recommendation as to what moisturizer to use. If anything abnormal is found on your skin, or if your doctor is worried for another reason, then you may get a referral to see a dermatologist