I am thankful your son is doing fine. Rest assured, he will completely recover, no lasting effects, except for a greater fear of snakes (especially by mom). I hate to hear it was while you were on vacation. Getting bitten by a water moccasin is extremely dangerous. Most times when they bite, they don't let go. While they are biting, they are releasing more and more venom.
Three years ago my son was bitten on the ankle by a copperhead on a Sunday afternoon. He really didn't feel it..thought it was a yellow jacket that bit him, but this friend saw the snake. I rushed him to the hospital 40 miles away in 20 minutes (I know the drive was probably as dangerous as the bite, but I was a scared mom). He did not receive any anti-venom; doctor said the side effects of the anti-venom was more dangerous than the effects of the bite. We spent 4 days in PICU watching his leg and foot swell til his toes looked like "little vienna sausages" and the doctor warning us we may have to cut a 12 inch slice in his leg to relieve the pressure on his skin. BTW, our bill without anti-venom was $110,000. PICU is EXPENSIVE!!!
It is remarkable how fast they recover though. By Wednesday, he was walking on crutches, by Thursday morning walking on his own, that afternoon we was jogging, and by Friday back at school with the nickname "Snake". That Saturday he was determined to play in his PeeWee football SuperBowl game. And he did. He made 1 touchdown and an interception.
Glad to hear your still had a good time on vacation and I hope you get to go back and have a real vacation soon.