Cleaning a metal water bottle can be hard, especially if you don't have a dishwasher. Since you can't reach to the bottom with a sponge, instead fill the bottle half-way with hot water and dish soap. Then, put the cover on and shake the bottle for a few minutes. Dump out the water, and repeat. After, fill the bottle up with regular water and shake. Pour it out, and then repeat this with just water until there are no more soap suds.