Chemical Desalination of Seawater?

amper writes: I've been studying seawater desalination products for use on board small yachts and life rafts, and the commonly available reverse osmosis devices are both highly expensive and difficult to operate. The only real alternative to a desalination pump for emergency use is carrying as much fresh water as possible, but this idea is not without its own problems. Is there some chemical process that could be easily packaged in a manner similar to the iodine and chlorine tablets that are sold for fresh water purification that would remove excess salts from seawater? What I envision is some chemical or combination of chemicals that would cause the sodium chloride, and possibly other salts or contaminants, to precipitate out of the solution so the now fresh water can be decanted.