Our food-grade stainless steel water bottles are highly rust resistant – not rust proof. We recommend cleaning the water bottle with warm soapy water, rinsing and letting air dry.
If your bottle appears to have rusted, it's probably just a mark left behind from the electropolishing process, which smooths the surface of the metal and makes it shiny. Sometimes electrolytes left on the surface turn a rust color, but it's harmless.
To remove residue, soak your water bottle overnight with hot water and baking soda or white vinegar. Follow the soak with a good scrub using a bottle brush or a scouring pad, combined with a wooden spoon or other kitchen utensil for leverage.