It could be that you have purchased a very cheap version of a plastic water bottle for runners and the plastic used in making it might be very low grade, it’s probably a good idea to upgrade to a better quality bottle. People have often reported that water left in low grade plastic containers tends to have an odd taste to it, I am not aware of any scientific research to back this up and no reports of people being made sick but to be on the safe side it’s worth investing a little extra money in a better quality bottle.