If you're left homeless by a rising river or the next Hurricane Katrina, your landlord does not have to put you up somewhere else. Even the flooding is his fault for not repairing a rusty pipe, he's still not obligated to find you a new home. You do, however, have other legal rights to fall back on.
Almost all states give you the legal right to a livable apartment -- one where the front door locks, the roof doesn't leak, the utilities work and the floor is solid. If a storm floods your apartment so badly it's unlivable, you can usually stop paying the rent and ask for any prepaid rent back. If your state requires you to notify the landlord in writing first, follow the notification procedure. If the law is on your side, the landlord may agree to find you another apartment rather than give up your rent check.
Flood damage that doesn't destroy the apartment can still make it legally unlivable, for example if it leaves you with no running water or electricity. If you notify your landlord in writing and he doesn't fix things, state law may entitle you to deduct part of the rent. If the damage is more minor, the landlord may disagree that you're entitled to a rent cut. It may take a trip to small claims court to settle things.
If you notify your landlord about a serious plumbing problem, she has a legal obligation to repair it, even if the lease says she doesn't. If you don't tell her but it's a problem she should have known about, the same applies. If a pipe busts because of her neglect, she doesn't have to offer another apartment, but you can ask her to pay for damage to your possessions. If she disagrees, it's small claims court again. When you request repairs, put it in writing and note the date. If you go to court, the paper trail helps prove your case.
Some states allow you to sue for flood damage if the apartment building has a history of floods and the landlord didn't tell you. In Oklahoma, the lease should inform you of any flooding within the previous five years. In any state, if you cause flooding -- you stuffed something down the toilet that clogged it, for instance -- your landlord may be able to sue you for damages. Taking out renters insurance to cover damages is probably better than hoping to get money from the landlord.