This is less of an issue if you're only putting water in your water bottle. You can either hand wash your bottle or throw it in the dishwasher if it's dishwasher safe. All water bottles come with cleaning instructions. But, if you're like me and putting electrolytes or other liquids in your water bottle, cleaning can get a bit more involved. This might require additional scrubbing with warm or hot water and typical dish soap. Pro tip: If mold starts to form, fill your bottle a quarter of the way with ice and add coarse salt. Shake it hard until whatever is growing on the sides of your bottle is removed. I have noticed the traditional Nalgene material is more likely to grow mold than new Nalgene materials and the 18/8 Stainless Steel. Another rule is to give your bottle a good scrubbing before using it for the first time.