It's really unlikely for two separate sources to have exactly the same information. There's usually something different -- a publisher, author, title -- for example, if you're citing an entire website, you may find it more useful to cite an individual webpage.
An example, taken from the Purdue Online Writing Lab:
For an individual page on a Web site, list the author or alias if known, followed by the information covered above for entire Web sites. Remember to use n.p. if no publisher name is available and n.d. if no publishing date is given.
"Athelete's Foot - Topic Overview." WebMD. WebMD, 25 September 2014. Web. 6 July 2015
If you hadn't already looked at the Purdue Online Writing Lab (OWL), it's a great resource for citation and style guide questions.
