Quote Originally Posted by Mist
Generally speaking, the basic difference between the words is as follows:

Водяной - containing water or consisting of water; in some rare cases may denote "wet".
I am afraid, it is too general. What about "водяная мельница" (water mill) and "водяная лилия" (water lilly)?

Quote Originally Posted by Dogboy182
Looks like водяной has to do with things that are living in water or need water to be sustained and водный is things that have to do with water or need water to take place?
+1

Not interchangeable.