It has been reported that a hot environment can create harmful levels of antimony oxide in PET-bottled water. Is that true?

There is no reason for concern. No studies have found any toxic amounts of antimony in PET-bottled water or containers. Unfortunately, there has been some consumer misunderstanding of studies showing higher-than-normal levels of antimony when water bottled in PET was exposed to extreme heat (80°C/190°F) for extended periods of time. Even then, the highest measured levels paralleled established safe levels for antimony in drinking water. In short, the very small amounts of antimony that might be found in PET-bottled water are of no concern and do not pose any health risk.