Eroc1_1 pretty much covered it. At day two, my runners "swam" in an inch and a half of 90 degree water in a cake pan for five minutes. /img/smilies/smile.png
My general guidelines were to have a clean, warm, dry brooder ready for their return from the water, to dry off any that did not immediately begin preening after bathtime, and to keep the water only deep enough to hit the tops of their legs - that was deep enough for floating or swimming, shallow enough to stand. The older they got, the deeper the water, the longer it took for them to get tired (when a couple of them just seemed to stand there, staring around, that was my signal to pull everybody back into "the bus" and back to the brooder. The bus was a deep cardboard box with a towel in the bottom, to get them from room to room once we began using the tub, at about day four.
I stood by every moment. Without full feathers and oils, they get soaked and don't float so well. But a few of them were excellent torpedoes! Enjoy those babies! They grow fast!!!