They're generally IP67 these days (verify before taking my word for it), which means they can theoretically be submerged in 1m of water for half an hour, but that doesn't mean I'd do it willingly. Also water droplets tend to mess with the tough screen and register phantom taps. Finally, when water gets in the speaker area (which is sealed) it generally makes the tiny speaker impossible to hear until it dries out, at least with earlier models.
TL;DR: while it may be designed to withstand that environment, it's not "ideal operating conditions" and probably not a good idea long-term.