Put your own feet in water and take a picture.
Or, look up photographic references.
It's impossible to find a tutorial on every single subject in the world, a lot of times you'll have to figure it out. Most of the time, you'll have to observe with what you do have and try to reference from that.
Morguefile is a good place to start. There's also
Stock.xchng. Heck, even
Flickr is a good source, just take care to not outright copy anything.