A few years ago, while I was out of town, DC experienced an atypical torrential rainfall. Upon my return, I was greeted with a basement that still had about six inches of standing water in several spots; there wasn't a dry section of the entire floor. In the end, the basement had to be completely remediated given the mold and water damage - an event that cost me just shy of $7,000 since I had no flood insurance.
Needless to say, I learned a lot:
1. That standard homeowners insurance doesn't cover flood damage
2. I'll never look at another basement the same again--I look for past damage in spots I never would have examined before
3. If I'm going to be out of town, I try to get someone to check in on my property every now and then to make sure nothing is going on
4. Check your drain pipes and make sure they're secure and positioned so they can't get nudged about and end up forcing water into places it shouldn't flow
5. Outside drain covers are essential!