Unless you are planning to buy property on the round floor in Venice, I would certainly not worry much about it. It can happen, yes, but it can also happen during summer (rather rate), spring and autumn. As a matter of fact, flooding of tourists is more predictable and frequent than "acqua alta". I fully agree with our Mod's opinion and I'd add to it that if it happens, you'll be able to shoot some really nice pictures that your friends and relatives will like!