I emailed them to ask about the storage. The answer was that heat and sun will likely cause chemicals in the plastic to leach into the water, and they don't know the effects of drinking water with those leachates in it. On a practical level, that's a conservative answer; they _don't_ know, and among the issues are how much of the chemicals it would take to cause any human damage and how much water you'd have to consume to get an amount sufficient to cause harm.