well i don't drink the water here.
disney is even registered to another country.i think they are registered in the bahama's. but they do what they can to prevent the spread. there are all kinds of hand washing stations, anti bacterial wipes are handed out all over the ships and given to each person that walks into a restaurant. the even have the stations outside the ship to use prior to going onboard. what they can't help is the person carrying the sickness onto the ship. and once in those kinds of close quarters the germs spread.
now what they could do is to refund your money if you are honest and the day you get onboard let them know you are sick. if they know you are ill prior to boarding, they will not let you on that boat. a doctor will see you to make that determination, however, from what i hear about that, 99% of the time, you are not getting onboard.
lots of folks do not get the insurance, and some will not cover this kind of thing. so after a family has planned for over a year, and paid thousands of dollars to go on this cruise, the day comes and a member is sick. well by then its too late, if you are honest, you will not be allowed on that ship and will not get your money back. so that family is not going to tell anyone they are sick, and get on the ship, they will not loose that kind of money. once on the illness can spreads.
last year when i went, i was disgusted by the amount of sick babies, i mean they were sick kids, and the parents still allowed them to go into the pool. granted the ships personnel should have seen it (if i did) and banned them to their rooms. but they don't. so i do see where the fault is the ship company's fault, however, the families are what brings the illness on board.