This is primarily due to the fact that the bottom Micro USB does not have a waterproof protective flap. (goodereader.com)
The Alpha is rated IPX - 4 for water resistance, so it can withstand splashes and even the shower (hence the importance of the charging port protective flap), but it shouldn't be in water for long periods of time. (pcmag.com)
All of these casing penetrations are covered either by the reflective side material itself, or by protective flaps that swing outward on wiggly hinges. (pocketnow.com)