How long will it take for me to see improvments in my skin and hair by drinking water? I currently drinl none and plan on drinking 3 glasses a day.

A few weeks. Not having any water is a very bad habit. You can survive on soft drinks but they don't hydrate you as well due to their so called solute content which promotes urination and more thirst. Skin takes weeks to grow and hair takes months so please be patient. They will improve in time and will feel bette too.
Many years. Unless you started out by being profoundly dehydrated to begin with, 3 glasses per day will make no difference in your skin and hair. Your kidney might appreciate it and your urine might change from darker to lighter yellow color due to dilution but that is the only change likely.You might check with your dermatologist if you actually have skin or hair problems that are obvious.