You'd have to read the individual policy, as JB said. However, there is flooding due to failure of household systems (i.e. the water line broke and my basement got 3 inches of water in it) and there is flooding due to forces of nature (i.e. 3 weeks of water caused the water table to rise and flood your basement as well as the entire town).
So it's not just enough to say "basement flooded". Certain types of water damage are covered; others are not. Read the "exclusions" paragraph(s) carefully.
Also, there isn't really a "normal" deductible for insurance. My guess that the majority of renters carry somewhere between a $0 and $500 deductible, but again, the average does no good if it's insufficient for that specific person's situation. If their washer is worth $400 and they have an "average" deductible of $500, then someone besides the insurance company is buying them a new washer.
My guess is you are tying to limit your liability due to a water loss of some sort. In the future, how about solve all of this with a lease clause: "LL is not responsible for damage to TENANT's personal property. TENANT's desiring coverage for their personal property are strongly advised to purchase a renter's insurance policy." --173.20.xxx.xxx