Here are several tutorials ive found that all appear at a quick glance to utilize all default PS tools, without having to resort to purchasing aftermarket filters

http://www.tutorialpark.com/waterdrops.php

http://www.photoshopsupport.com/tutorials/cb/water-drops.html

http://www.n-sane.net/tutorials/water_drops/index.php

found these doing a Google search for "photoshop tutorial water"

If youve any aftermarket filters enhancing your APS, these may help automate the process :)

Hope this helps,

Logan