Stainless steel glasses are BPA-free and safer than plastic cups. It doesn't cause poisoning: Aluminum glasses can cause poisoning if the lining degrades over time, while stainless steel doesn't.
If you want to ensure safe drinking, reusable steel water bottles, look for #304 or 18/8 food-grade stainless steel. #304 or 18/8 food-grade stainless steel is safe at all temperatures and will not immerse chemicals in water if scratched or aged.
But in the market, there are some cheap cups which is made of 201 stainless steel, which is not food-grade material, may cause disease in the future. And consumers cannot distinguish from their appearace. Only using the chemical to check is it made by 304 or 201 stainless steel.
