water is water, you won't die immediately form drinking water that has been around for 6 months, if you can filter and/or boil it, it is still water. You might have some toxins or bacteria in the water, adding a little bit of high proof alchohol (liqour) to top off the bottle may help.
you could shock it but personally I'm not a fan of chlorine shocking water.. with bleach I have a 0.02 micron filter
I'd sooner pour old piss in it and inhale, well not really but it is a lasts resort.
So yes you can use water that has been stored for more than six months. Last year I drank my full container of more than 6 month stored water and I'm still alive. It was actually 8 months old so, if you are in a disaster and your like I CAN'T drink that bottled water it has been stored for more than 6 months, slap yourself hard and drink it, purify it if you can but DO not for a second think water stored for more than 6 months will kill you, drink fresher safer water sources if you have them but it is still better than piss, which if also is not desalted will also dehydrate you.. drink the water not the piss. its only BPA's people have been getting this stuff in plastic bottled stuff for years and cancer rates are not an epidemic. bacteria is free protein, if you can't see it just eat some mushrooms after or a little silver, or some vodka, works for spetznatz.. run it through a silver footed antibacterial militia sock if you have to or some level 2 ecws undies or shirt. I'm pretty sure they are all antibacterial treated.
bpa plastics are apparently banned in Canada now anyway, in baby bottles ....