An animal water supply system includes disposable containers such as plastic bags that can be supplied in bulk in sterile form and filled under a change hood or other sanitary environment using a filling machine located in the sanitary environment. The containers preferably comprise plastic bags configured to be suspended from a hanger of a bag filling machine. The machine's hanger is preferably configured to support a plastic bag during both bag filling and the subsequent insertion of a watering valve into the bag. The bag is further configured to permit its placement in or on a conventional cage while protecting the tearable material of the bag from the animal. If desired, a liner can be provided to further protect and support the bag or other container on a wire bar lid.