The salt in the water will remain behind and will kill them

some plants are more tolerant then the others. I live in the building that softens all incoming water, so i have no other since may be 3-4 years. fortunately i am snow birding and so i took most of my vulnerable plants South. However more then enough makes do with softened water ...4 years running and they are OK so far. not saying they will continue to be OK , but just they can take it.

I rarely top water since all my plants are on water wicks and are sub-irrigated in passive hydro. I of course converted all of them long time ago and am using fast draining jungle mix that i mix myself. don't know if that plays a role or not...

these are the plants that do OK so far in nothing but softened water:

several Ficus lyrata, several Ficus alii, a dozen Jades, several Bromeliads (Guzmania, Achmea, Vriesea), hawortia, many Cacti, Cycads, Philodendrons, large mature Aralia,

syngoniums, African Masks (Alocasia), Calamondin.

i fertilize using acid-formula MG for plants that need it. or other ferts also in water solution.

Naturally they don't get flushed in winter when i am not there. But i do flush once i am back and take them off wicks for a month or so and then top water. then back to wicks.

Some smaller tropicals i bring back up for summer from FL, so half a year they get muni Miami FL water half year NJ muni softened water and they are fine too:

begonias, Crotons, Aglaonemas, Dieffenbachia, tropical Hibi's, Phalaenopsis orchids, Caladiums, small Aralias, small African Masks (Alocasia).

the plants that get brown edges on leaves and are well known to be sensitive to salts i water with spring water wherever they are stationed :) :

Calathea, Cordylines, Dracaenas.

there are 2 types of softeners and i don't know which one i have : no matter how many times i ask ..so perhaps mine is the one that is less harmful since my plants do fine with it??

..may be eventually i can get an answer from management :(...but it is not pressing, since plants are managing so far...

there are too many variations on the theme.. for us to answer your question.. when all you tell us is that the water is softened ...

i use a salt system.. i am not dying of hypertension.. and neither are my plants ... the salt is used to BACKFLUSH the filter membrane ... and is then rinsed away ... it does not end up in your drinking water.. period.. if so.. most of us on wells would be dead ...

tell us specifically what you are using.. and maybe we can google it up for you ...

you might also contact you LOCAL COUNTY Ag or extension office.. and ask them general questions about the water in your county .... and if they are aware of any blatant issues ..

you should also ask them where to have your water tested.. and test it before and after your water system ... a real estate office will probably be able to tell you were to have it tested ... as i seem to recall i had to have mine tested 22 years ago.. when i bought this house ...

ken