Configuring Webmaster Tools Preferred Domain
Google Webmaster Tools allows you to indicate a preferred domain for your website. There can be up to four variations of your domain and indicating which domain should be used as your primary domain is one simple step you can take to improve what Google knows about your site.
This tutorial will demonstrate how to indicate your preferred domain.
Request access to the client Webmaster Tools account.
Click here for instructions from Google how to do this.
Once you have access, log into the Webmaster Tools portal and select the website profile you want to work on.
Click the gear icon on the right side of the screen and select the "Site Settings" option. It will bring up the screen below.
Indicate which URLs you would like as the preferred domain. It does not make a difference if it is the www or non-www version. Whichever you choose needs to be consistent with the structure you use on your website.