There is typically always at least 1 water park open on any given day at Walt Disney World. Typhoon Lagoon is currently closed for refurbishment, so that only leaves Blizzard Beach for daily operating hours. Disney has announced that Blizzard Beach is planning to close on January 23rd due to projected low temperatures. For guest and cast safety, as well as to prevent wasted operational costs due to low attendance, the park will close on this date.
Disney does have to close the water parks every now and then due to low temps even in Florida. Most of the pools at Walt Disney World are heated, but in cooler temps, it can still lead to issues. The water parks also go down for refurbishment each year during the off season. The two water parks take turns undergoing refurbishments for a couple months so that the other park will remain open.