BC, you can definitely walk through the water stops. Just show the same consideration to those behind you as you would if you were slowing or stopping on a bicycle. Signal your intentions and be aware of traffic behind you. And remember that, especially late in the race, people behind you may be fatigued and maybe not paying as close attention as people in a paceline might be, either.

But one thing I really found valuable was entering a small and inexpensive 10-miler about two months before my first half, not really racing, JUST for practice drinking water from aid stations.

When it came to the actual race, I was really, really, really glad I had that practice. There's definitely a technique to drinking quickly out of a cup while you're breathing hard, which you will probably be even if you're walking. (The usual method is to pinch the cup to make a spout, tilt your head and pour the water into your cheek. Then you can swallow between breaths.)