After repeated long term use of any container filled with alkaline water, minerals will start to create a thin harmless coating of calcium and magnesium inside the surface of your travel container. These minerals can be easily wiped clean with a soft cloth if they build up after long term usage of the container. If the container is only rinsed with soapy water, especially containers with a narrow opening, then soap will tend to stick to any minerals left on the inside surface. Overtime, this can impart a soapy taste back into the alkaline water when the container is reused. As a result, it's good to be able to reach inside your container to physically wipe the inside surface clean. You may not notice any mineral build-up until after refilling the container for about 20-30 times or more, otherwise you may want to get in the habit of wiping and drying the container after each use.