If you will be putting them in water, does it make a difference in any respects e.g. time to dissolve, what is better from health perspective and so on, does it make a difference to absorbtion, just wanted to know the various differences.
IMHO, salt is salt when dissolving in water, albeit the finer the grain, the more rapid the dissolving, though in either case, it will be FAST. Salt, in all its forms, tends to absorb water, even from the atmosphere.
Try it for yourself. Use a tall, quart container, preferably clear, add a tablespoon of salt and see how much reaches the bottom. Try it with large crystals, i.e. kosher salt, and fine crystals, i.e. normal table salt, and see if there is any difference.
Finer salt will dissolve more quickly than coarser. Rate of dissolution also depends on temp and concentration. It's very unlikely you'd see a practical difference in the respective rates of coarse and fine salts.
If you're cooking the salt into soup, it won't matter at all; both will fully dissolve into solution until the solution reaches its saturation point.
Dissolved salt is dissolved salt. It doesn't matter whether the crystals were fine or coarse, or whether it was evaporated sea salt or mined.
FWIW, all salt was sea-salt at one time or another.
Other than temperature the rate of dissolution is a function of surface area. The exact same quantity of salt in large crystals exposes less surface to the liquid than does smaller or ground salt. Think of the given quantity of salt as A. one large crystal as opposed to a fine grind salt. Just plain old logic tells you it would take a lot of stirring to dissolve that big salt crystal.