Repeat frequently, drink what you can hold.
It got me through 5 days of a nasty bug like this. Gatorade or sports drinks are good if you have them.
Geez, the got Norwalk virus BEFORE stepping on a cruise ship.
Surprisingly, Gatorade lists the RDA's of Sodium and Potassium. The RDA for Sodium turns out to be the equivalent of about 2.5 gpd (grams per day), while Potassium is higher, at about 3 gpd.
Dietary studies have shown that most adult Americans are deficient in Potassium. I remedy that by using salt substitute, which is Potassium Chloride instead of regular table salt.