text: why does bottled water have a spoil date on it?   you are going to love this.. the water doesn't go bad... the bottle does. :) the platic breaks down, slowly.. so that after months adn months of sitting there, the water starts to have enough plastic molecules floating around in it that you can taste it. try drinking really old bottled water, you will get a disgusting sticky kinda film on your mouth - that's plastic. i don't know if glass bottles of water have that or not, glass breaks down too, but it's not nearly as soluble in water.