driving through a water poddle will dislodge p/s belt

Could be a weak tensioner or worn out belt. Water isn't good but it shouldn't come off that easily. Alex

I don't think they have normal puddles of water in Dallas TX from what I remember

For 'some reason' - the belt is wanting to run off anyway - water just makes it easier to do so. This will req *hands-on* inspection / evaluation by qualified personnel. Keep in mind once a serpentine belt runs off track - it will continue to do so unless it is replaced.