(a) in or immediately adjacent to toilet rooms or their vestibules; and

(b) in food preparation and warewashing areas or in an otherwise readily accessible location for use by all employees working in these areas.

Sinks used for food preparation or for warewashing shall not be used for washing of hands or for any other purposes; provided, however, that such sinks may be used for other than food preparation or warewashing purposes in instances where such other use would not adversely affect public health and safety and has been approved by an authorized department representative.