Create a file named ".htaccess" at the root of your website. Add the following command in the file:
AddCharset UTF-8 .html
Replace UTF-8 with the character set you wish to serve the pages in, and .html with the file type that this applies to.
This setting will also apply to subdirectories of the directory where the .htaccess file is placed.
For more information see W3C: Setting charset information in .htaccess