how did they cleanup after Aqua Alta in Venice

I happens often, I'm not aware of any disinfectant (where did you hear this??) - the hose is the usual method.... they are used to it and it is routine...

I thought restaurants gave that water to foreign customers who asked for tap water instead of paying for bottled mineral water.

The lagoon is salted, so they need to wash their shops using fresh water to avoid everything to rot and smell like a swamp.

When it's dry, I suppose they wash with detergents like any other morning. It's not that shopkeepers wash the floors only after a flood-
You do it almost every morning, high tide or not. What do you think swims in the lagoon, the black plague virus? Anything else is killed by the professional detergents used by all shopkeepers all over the world.

I'm starting to hate the worlds "I heard that".

it is amazing how quickly Venetians clean up and dry out after acqua alta. Venice is very clean. Yes, everything is hosed down and in some places you can smell disinfectant after an acqua alta subsides. I was there during the extremely high flood in October 2018 and had a wonderful walk around the neighborhood the morning after a somewhat traumatic arrival. The coffee shop that I landed at had a pump and hoses and squeegies and disinfectant. The regulars were coming in for their coffees even while the clean up was still going on. My sister and I enjoyed our cappuccino and watched very closely. The proprietors were doing the clean up, one young man was taking care of the customers. The proprietors kept the cleaning going away from the bar, obviously careful about cross-contamination, and the barista kept his area very clean. He even did a quick hand wash after handling the money, so he would do a big round of coffees and pastry, then take everyone's money, wash, and start over. One last thought about the ground floor, if you treat the ground floor just as you would the walk ways out of doors you won't be disenchanted. I have never found a Venetian restaurant unclean. If you are visiting during a time when Venice will flood every day, twice a day, just be prepared.

Dario: Thanks for the feedback. I did not know anyone from Venice, I could only rely on newspaper or internet to learn as much as possible about any city on the other side of the globe. It is nice to hear from you- a local residence who knows what is going on in front of your eyes.

Rene: Your detailed feedback is very precious and important to us. By sharing your experience, we learn the first-hand information which could not be found on the news or internet. Thanks!