Are you aware that search engines treat the URLs http://www.yourdomain.com and http://yourdomain.com as two distinct websites though it refers to the same website.

This create the issue of duplicate content as seen by the search engines since search engines are unable to resolve canonical issue.

One way to work around this issue is by adopting one version to display your URL, that is, either the www version or the non-www version.

For domains that are hosted by Linux-based web servers, you can modify the .htaccess file to re-direct non-www to www or www to non-www.

Below is the additional instructions to be added into the .htaccess file if you want to re-direct non-www to www.

RewriteEngine On
RewriteCond %{HTTP_HOST} ^yourdomain\.com [NC]
RewriteRule ^(.*)$ http://www.yourdomain.com/$1 [R=301,L]

To re-direct www to non-www, the instructions is as follow.

RewriteEngine On
RewriteCond %{HTTP_HOST} ^www\.yourdomain\.com [NC]
RewriteRule ^(.*)$ http://yourdomain.com/$1 [R=301,L]