i live in SD where we have Scripps Ocean institute. the provide free FILTERED water for the general public. and lots of people here use it with no problems. but they do wait a few days after a storm or when there is a black tide.
so you can, but is has to be filtered. which is expencive, time consuming. better off buying a very good salt mix. i use tropic marin. IMO its good salt. but opinions may vary here...
good luck.
a few words of caution.
nothing happens qiuckly in saltwater other than death.