Water can go bad, particularly in a plastic bottle that has been left in heat, or if it has been stored longer than six months. The chemical bisphenol-A can spread from a plastic bottle into water if temperatures get too high. BPA is dangerous because it can interfere with hormones.
Plastic water bottles are not intended for reuse. Metal and glass containers are better options.
After water is stored for about six months, bacteria and algae develop. That time frame is shorter if the water is being kept in a sunny or heated spot, or in unclean containers. In general, people should store water in their basements for no longer than 12 months.