Well, first of all I recommend taking your own hot water with you in a Thermos. It will keep just-boiled water hot enough for green tea (about 75°C) for an entire day. That will be easier than having to go far out of your way for water or a means of boiling it.
(Just remember that many Thermoses nowadays are so good that even after a half-day, the water inside may be too hot for green tea, so before steeping your tea, pour the water into your cup and let it cool for a couple of minutes.)
If water in the Thermos gets too cool, you could always "touch it up" with a microwave oven, if one is available. (I usually do not recommend microwaves for heating tea water simply because of the plethora of food smells that lurk in most microwaves.)
To keep your water hotter even longer, you can pre-warm the Thermos: Pour boiled water inside, let it sit there for about 5 minutes, pour it back into the kettle and re-boil, then pour it back into the Thermos. Sometimes those last 10 degrees of heat make a huge difference when brewing on the road.
And instead of a teapot, I would take a long a mug and an in-the-cup infuser like this one.
With these three things (plus the tea, of course) you will be a completely self-contained lean, mean brewing machine — with no need to seek out electrical outlets or water sources or microwaves, etc.
A couple of final points: I wouldn't put brewed tea in a Thermos, because the tea's taste (and catechins) degrade quickly inside. And as for those commuter mugs with a built-in infuser, the problem is that the mug part is almost always made of plastic, which I do not recommend for tea.
Happy on-the-road brewing!
That's another way to do it.
blog feed, facebook, reviews, steepster, teas, tweets, videos