teetotaler is a corrupted spelling of tea totaler, meaning that, in colonial times when liquid beverage options were much more limited, one either drank tea (a drink so popular that colonists revolted when the British imposed a tax on tea imports leading to what we call the Boston Tea Party) or drank wine and other alcoholic beverages like ale and whiskey. If one chose, for religious or other reasons to abstain from alcohol, then you drank tea exclusively, hence a tea totaler