I recently implemented deflate on apache following recommendation from Google  PageSpeed Tools

https://developers.google.com/speed/pagespeed/

STEP1

Find your apache configuration httpd.conf

SSH to your server and run this command

$ ps -ef | grep apache

then run

$ /usr/sbin/apache2 -V

Find your apache configuration in my case CentOS it is located at

/etc/httpd/conf/httpd.conf

STEP2

Enable mod_deflate by modifying httpd.conf

http://www.brighterlamp.com/2010/10/how-to-enable-mod_deflate-on-apache-to-optimize-page-speed/

# mod_deflate configuration

<IfModule mod_deflate.c>

# Restrict compression to these MIME types

AddOutputFilterByType DEFLATE text/plain

AddOutputFilterByType DEFLATE text/html

AddOutputFilterByType DEFLATE application/xhtml+xml

AddOutputFilterByType DEFLATE text/xml

AddOutputFilterByType DEFLATE application/xml

AddOutputFilterByType DEFLATE application/x-javascript

AddOutputFilterByType DEFLATE text/javascript

AddOutputFilterByType DEFLATE text/css

# Level of compression (Highest 9 - Lowest 1)

DeflateCompressionLevel 9

# Netscape 4.x has some problems.

BrowserMatch ^Mozilla/4 gzip-only-text/html

# Netscape 4.06-4.08 have some more problems

BrowserMatch ^Mozilla/4\.0[678] no-gzip

# MSIE masquerades as Netscape, but it is fine

BrowserMatch \bMSI[E] !no-gzip !gzip-only-text/html

<IfModule mod_headers.c>

# Make sure proxies don't deliver the wrong content

Header append Vary User-Agent env=!dont-vary

</IfModule>

</IfModule>

STEP 3

Restart Apache

/sbin/service httpd restart

STEP4

Test to make sure deflate is working correctly  by going to this website and test your URL

http://www.gidnetwork.com/tools/gzip-test.php