The 2006 International Building Code requires drinking fountains in all occupancies except dwelling units and and sleeping units. This section of the code has frequently been overlooked. However building departments have begun enforcing the requirement with some regularity.
Generally you are allowed to tie your drinking fountain into a kitchen sink but it cannot be part of a service sink. I have seen kitchen sinks without drinking fountains pass but this isn’t spelled out in the IBC. In fact, even restaurants are required to have drinking fountains.
In occupancies where drinking fountains are required the required number is generally 1 per 100 occupants. There are a few exceptions. Visitors in institutional settings need 1 per 500. Mercantile and storage occupancies require 1 per 1,000. Factories require 1 per 400.
The image is from the ADA guidelines and shows required dimensions for accessible water fountains.