Can I drink old water?!

You'd be better off getting some new water. It wouldn't do you any good. Tiny bits of plastic from the bottle go into the water over time. If enough was in it, it could be toxic, but that would take a lot of plastic and a lot of time. It probably wouldn't taste very nice, and at worst it could make you ill, but I doubt it would kill you.

It probably won't kill you, but it's got bacteria in it now. Better to pour out the water, recycle the bottle, and get yourself a clean glass of water.

If it has been unopened and its still before the best before date printed on the bottle somewhere is it is ok to drink.

If you drank from it and then left it under the bed I would not chance it.

go down to the chemist and get water purification tablets, and then boil it and add the tablet, should be ok, but then you could just empty it down the sink and drink some fresh water?

Yes as long as the seal is intact.

Best before date? With water its a joke.. As long as there is no degredation in the container you could drink it in a million years

How old do you think the water in your taps is? Probably several hundred thousand years I would guess.

of course you can drink it. now whether its safe to drink is another question.

Yes you can

If it doesn't taste nice or smells off, its flooded with bacteria, don't drink it.

you could but i wouldnt if i was you
in that time (if it was opened before) there will be so many bacterias....oh nooo

No, its now a deadly poison. What do you think?