4 cups water
2 inch piece of fresh ginger sliced very thinly
1 lemon or lime
1 or 2 tablespoons honey or agave or maple syrup
Boil the water and ginger together for at least 20 minutes.
Strain the tea, discarding the solid ginger.
Add the juice of one lemon or lime and sweetener to taste
This stuff is magic. Drink a couple of cups on the way to the swimming site and it will heat you right up. And a thermos full of it for after the swim, when you really need it, just can't be beat.
It will make you a superhero in cold water.