Rubin also noted in her report that the tumbler is specifically meant for cold water — not for hot or acidic beverages like coffee, because of the nickel content of the stainless steel used. Nickel is another metal that can be seriously harmful if ingested, but it takes a lot of time for the metal to actually contaminate food or water. Both heat (from beverages like hot coffee or tea, for instance) and acids (like those found in citrus fruits and soda) can speed that process up. Sticking to plain water removes that risk.

Fascinating.