Mineral Water heals over time as long as your character touches it, and the healing effect will last for 2-3 seconds after leaving the Mineral Water. Characters will not drown when staying under Mineral Water, but they will slowly float up just like in ordinary Water and most other liquids.
You can multiply Mineral Water infinitely by placing a drop on the ground and only scooping up the offsets, not the source/core you placed (just like you can do with any other kind of liquids too).
Mineral Water can be placed and stepped into so it can serve as a healing pool.
Mineral Water can also be used for watering Crops (the block with the liquid has to touch the tilled land with the Seeds at least corner-to-corner). Mineral Water will not freeze in cold areas, but usually seeds will stay fallow there anyway if it's too cold for crops to grow.
Mineral Water can be used for cooking healing Food in the Cooking Station, like Wholesome Bread, Wholesome Soup, Wholesome Sandwich and Wholesome Pie. Pets might prefer Wholesome Bread as their favorite food.
Mineral Water can also be used as elevator when digging directly downwards from the surface from within a small pool of Mineral Water; even safely down to the deepest layers. In that way you can "climb" up again without any extra-work and no need to place ladders or so, by just swimming upwards in the falling Mineral Water again, as your character cannot drown in Mineral Water.
You can also place Mineral Water onto the border of some platform or building high up, and it will drop down in shape of a small waterfall that you can use as an elevator, if you are careful to stay directly within it.
You can also use Mineral Water (like ordinary Water) as sort of a safety sheet to jump in from high up; only 1 block of Mineral Water (or Water, or Bog Water) is enough to catch your character's fall and keep him/her from dying (currently, as of R26 in December 2015).
If you purify Corrupted Water by either using Purification Bombs or Healing Beacons, it will turn into Mineral Water. Mineral Water can kill corrupted creatures if they touch it for too long. Mineral Water itself cannot purify corrupted blocks any longer when touching them though.
Mineral Water will not harm any other type of creatures than corrupted ones, in fact it can even make night creatures stay alive in the sunlight if they should happen to get stuck in Mineral Water somehow.
Mind that Mineral Water alone will not make the corruption-scale go down or away, but Healing Beacons can if the player-character touches them directly (like standing on top of them).
Also Mineral Water will neither cool the character on the Lava layer nor will it warm the character in freezing areas like Taigas, Frozen Desert, frozen Oceans, snowy Tundras or the like. However, in some cases Mineral Water is sufficient to cool down liquid Lava into Hardened Lava, and Hardened Lava into Igneous Rock.