From "The Care and Feededing of a Sailing Crew" by Lin Pardey...
"...salt water can be used for cooking. One cup of sea water has approximately two rounded teaspoons of salt in it. For bread baking, substitute one cup of salt water for one cup of fresh. Boil eggs in 100 percent salt water, cook rice in one-third salt water, two-thirds fresh. For dried beans, don''t usee any saalt water at all or they''ll stay tough. "