The Answer
It has nothing to do with “tea”, but rather refers to total abstinence from alcohol.
I had always assumed that those who abstained from drinking alcohol were called tea-totalers and that somehow that translated into “drinkers of tea”. I never considered how totaler becomes “drinker of”, but figured it went back to Latin or Greek.
It turns out that this is not the case at all. It has nothing to do with tea.
The key part of the word is total and refers to total abstinence. So a teetotaler is not just casually choosing not to drink. They are pledging total and complete abstinence.
At the time the word came into use – in the 1830s – some temperance societies didn’t see anything wrong with wine, beer, or cider. The harder-line abstainers advocated for total abstinence from alcohol in any form.
What about the tee ?
… likely, the “tee” that begins the word teetotal is a reduplication of the letter “t” that begins total, emphasizing that one has pledged total abstinence. In the early 1800s, ”tee-total” and ”tee-totally” were used to intensify ”total” and ”totally” much the way we now might say, ”I’m tired with a capital T.”
In my younger days, I would occasionally find myself “drunk with a capital D” because I drank too much “beer with a capital B”. Not so much anymore (with a capital A).