Of course water is probably all your basement will ever see, but think about long term reliablity and ease of testing, fewest components, etc. This kind of application can help save you a ton of $$ in damage and the the sensor portion needs to be as failsafe as you can come up with. I still vote the simple float switch if it was my basement. Basements are rare in California but sump alarms are common.
Now what I need is an earthquake alarm circuit that gives about 5 mins warning of a big one
Lefty