A bowl is a dish that all food and drink is served in. The bowls change size according to how many pets are in your home. In Nintendogs + Cats you have the option to change what kind of bowl you use via the description of a food or drink. When you look at a food or drink's description, in the top-right corner of the description box, there will be a picture of the bowl that you are currently using for that food or drink with left and right arrows on either side to scroll through your options.
Regular food starts out served in a white bowl, diet dog food and milk start out in a wooden bowl, diet cat food starts in a pink-and-white polkadot bowl, and water starts out in a silver metal bowl.
Some bowl styles are exclusive to certain foods. For some types of bowl, the one used for food is more round while the one used for drink is more square. The wooden water bowl is different from the wooden bowl that diet dog food starts in.