Water is used in Christian baptisms: you get your head (or your whole body) dunked in water, and when you come out of it, you're a legit Christian. Here's what Ames has to say about it:
When I was in seminary I used to go sometimes to watch the Baptists down at the river. It was something to see the preacher lifting the one who was being baptized up out of the water and the water pouring off the garments and the hair. It did look like a birth or a resurrection. For us the water just heightens the touch of the pastor's hand on the sweet bones of the head, sort of like making an electrical connection. (1.5.16)
Ames is intimately acquainted with baptism because he performs the ritual all the time. Unlike other people, he gets to really feel what it's like to actually touch the heads of the new Christians. It's a powerful feeling for him.
For Ames, though, the miracle of baptism can be seen in everyday events, too:
You can Tobias are hopping around the sprinkler. The sprinkler is a magnificent invention because it exposes raindrops to sunshine. That does occur in nature, but it is rare… you two are dancing around in your iridescent little downpour, whooping and stomping as the sane people ought to do when they encounter a thing so miraculous as water. (1.5.16)
The point is that while baptism as a ritual may be a one-time-only thing, the idea behind it—that the world is sacred, and so is everyone in it—is present everywhere and at all times, if you know how to look for it.