Crossing streams of water runoff on a curvy descent can be nerve wracking. About the only thing you can do to safely cross water on the road is to be as upright as possible to maintain as big a contact patch as possible. This is hard to do when you're already cornering and banked over on the bike, so what I do is overcorrect for that curve, straighten up for as straight a line as I can manage across the stream, then correct my lean on the way out. Still, you never know what's under that stream of water, which makes it nerve wracking. The other thing I have to worry about is getting splashed by cars, so I try to slow up when one passes me so they take that stream without me beside them. I'm getting gritty enough on wet road as it is, so I really don't need their help for more wet grit.