I am currently using bottled seawater to hatch my brine shrimp in which I bottled in 1995...
I had a little pet shop at the time and our SA black culture has it that if you drink sea water, it removes evil spirits from your home and clears your systems etc. etc..... So, I bought 1000 empty bottles and paid my kids 10cents for each bottle they filled during my sea holliday in 1995.... They sold like hotcakes, but then I moved (and closed the petshop)
Ever since, These (remaining) about 700 x 500ml bottles have been moving around from house to house with me (and being stored outside everytime)
The water is as fresh as if it was bottled yesterday.... The secret being, that at the bottom of each bottle, I added about half inch of seasand before filling the bottles.... I believe in this way, seawater can be kept indefinitely.