My house is on a slab and has a tiny crawl space has little water...?

my crawl space vent in the main bathroom has little water in it! I only saw it today. the rest of the vents are dry. We had a really bad rain storm a week ago and it could be that. I have lived here for 10 yrs and this is the first time I have seen water. sure is strange. what should i do? help?? should I just drain it out? or let it dry up by it self..