It isn't an element, it is the salt sodium chloride a compound.
boron
Yes sodium chloride may be used in water softeners.
No. Calcium carbonate is one of the minerals that water softeners are supposed to eliminate, or at least reduce.
There are no chemical elements as such in eyewash. Most eyewashes are a mixture of water and witch hazel. Witch hazel is extracted from the leaves and bark of a species of shrub and contains a mixture of chemical compounds, most of which are made up of carbon, hydrogen, oxygen and nitrogen ions.
Using an eyewash that is produced to be used as such is safe, if used according to the directions. Homemade eyewashes may be harmful. It is always best to use an approved eyewash.
Eyewash is used to get debris out of the eye. Like if your eye felt like something got into it and it was hurting then you would need to use eyewash or just rinse your eye with water to remove whatever had gotten into it.
Boron
Boron which occurs in nature as Na2B407 times 10H2O which is also known as borax. H3BO3 which is boric acid is a weak acid eye wash.
Eyewash stations should be no more than 10 seconds walk from where chemicals are used and splashed may occur.
When water is hard, meaning it contains more minerals than ordinary water, you would want to use a water softener. Water softeners remove minerals from hard water, which would normally clog drains. Water softeners are normally used if water contains a lot of calcium and magnesium in it. The softener filters out the calcium and magnesium to make the water "soft".
Precipitation is used to remove unwanted ions most commonly in water softeners. Sodium carbonate is added to the water to precipitate calcium carbonate.
Most water softeners remove calcium and limestone. These are not really harmful to humans, but cause a scaly build up in pipes and tanks.