There are 2 techniques I'm familiar with to get fresh water from salty water. The first, is boiling. You should boil the salted water and catch the steam. The second is by freezing. In cold/freezing conditions, put some salted water in a container. The fresh water will freeze first and the salt will concentrate in the middle. Separate the fresh ice to get some fresh water. Otherwise, you can always buy one which uses electrolytes and chemicals.