Desalinating salt water is one way arid regions are able to obtain drinking water. however, it's not an easy process.

a. if you were on a boat why can't you drink salt water to survive? how could you desalinate small amounts of water for survival?

Drinking Salt water would dehydrate you making you more thirsty and eventually you'd die. You could desalinate small amounts of water by distillation with the appropriate tools all you'd need to do is heat the salt water and catch the vapor/steam in a different container. This could be done slowly using heat from the sun and clear plastic water bottles if no other heat sources are available. the salt stays in the heated container while the vapor/steam is desalinated drinking water.