To assess their safety, we would need to know what chemicals are in the bottles, not just that BPA is not. After all, other toxins are used to make plastic, including, sadly, FDA approved ones.
In the case of Tritan, the chemical ingredients are unknown. Neither the bottle-makers nor the Eastman Company, which manufactures Tritan, will disclose them.
The same is true of Sigg’s aluminum bottles. They are lined with a mystery material whose ingredients Sigg will not reveal.
In the absence of information, a reusable plastic water bottle made with HDPE, LDPE or PET would be a safer choice. (Nalgene actually offers bottles made with these materials, too, as do many other companies.)
Or, if you’re worried that plastics, in general, have not been adequately tested, use a stainless steel bottle. Both Klean Kanteen and New Wave Enviro offer stainless bottles with a choice of plastic or stainless tops.
For more, read my latest This Green Life column : “Plastic Water Bottles: Is BPA-free the Same as Safe?“