When using stainless steel cookware, know that deeply scratched and pitted pans can cause metals (nickel and chromium) to migrate into food in trace amounts. These are not toxic elements, so there is not really cause for concern unless you have a specific allergy or sensitivity.
Hereof, is it OK to put lemon in a stainless steel water bottle?
It is durable, won't leach chemicals into your beverages, and does not retain flavors or smells. Additionally, it's perfectly safe for lemon water! Even acidic beverages are safe to use in stainless steel bottles (unless in very high heat and even then it's mostly a concern for people with nickel allergies).
Are Yeti cups safe to drink from?
Legendary YETI durability doesn't stop inside your dishwasher; thanks to rugged 18/8 stainless steel construction, your YETI cup is safe and sound. And because each YETI cup is BPA-free, there's an extra emphasis on "safe." But your YETI tumblers and bottles are built to handle almost anything, no matter your plan.
Can there be lead in stainless steel?
First, there is no lead used to make stainless steel. Stainless steel does contain other toxic metals (see Q&A: Stainless Steel Leaching into Food and Beverages), but it does not contain lead. It may even not even set up correctly if they added lead to the formula, so I doubt that any stainless steel contains lead.