Borrowed from an email passed along to me on English history…
There is an old Hotel/Pub in Marble Arch, London which used to have gallows adjacent. Prisoners were taken to the gallows (after a fair trial, of course) to be hung. The horse drawn dray carting the prisoner was accompanied by an armed guard, who would stop the dray outside the pub and ask the prisoner if he would like “one last drink”?
If he said yes, it was referred to as “one for the road”.
If he declined, that prisoner was “on the wagon”.
But there’s a conflicting etymology for “on the wagon”…
Another explanation comes from the early 20th century temperance movement. The phrase “on the wagon” began as ‘on the water-cart’, migrated to ‘on the water-wagon’ and finally to ‘on the wagon’. Water wagons trolled the streets during that time, not carrying drinking water but water for damping dusty streets during dry weather. Those who had vowed to give up drink and were tempted to lapse said that they would drink from the water-cart rather than take strong drink.
