Plastic is safe depending on the type of plastic used.
check the recycle label on the bottom
#1 ok for one time use, but not to refill, there is slight chemical seeping over a long time ( months )
#2, #4, #5 are safe to refill and don't seep
#7 ( colorful ) known to seep rapidly, and can cause unwanted hormonal effects ( see text below )
Most bottled water is #1 which is very cheap to manufacture, next time you buy bottled water you might want to check to make sure it hasn't been sitting on that palate at Sams Club for a couple years.
Unfortunately, those fabulous colourful hard plastic lexan bottles made with polycarbonate plastics and identified by the #7 recycling symbol, may leach BPA. Bisphenol A is a xenoestrogen, a known endocrine disruptor, meaning it disturbs the hormonal messaging in our bodies. Synthetic xenoestrogens are linked to breast cancer and uterine cancer in women, decreased testosterone levels in men, and are particularly devastating to babies and young children. BPA has even been linked to insulin resistance and Type 2 Diabetes.