To create sprites there is a program called sprite explorer, it has a special wizard built in it allowing you to make sprites step by step, provided that you know how to create the images.
The hl sprites have a rule that their dimensions must be 2,4,8,16,32,64,128 etc, you get the idea, but they do not have to be square, you can make a sprite 64x32 for example if you wanted to.
Another thing you must keep in mind is that sprites need a black background, otherwise they won't get transparency.
To create an animated water texture there are two ways:
1; the scroll way, If you put SCROLL in front of the name of your texture and then place it within a .wad using wally (wally is the software for creating .wad files), it will have the scrolling effect in game (the scroll effect is when the texture slides in 1 direction). Ofc the texture would also have to be seemless.
2; the animated way. There is a way to make textures animated just like sprites frame by frame, to do this you have to name the textures like this before importing them into wally and compiling them:
+0texture1
+1texture1
+2texture1
+3texture1 etc, with maximum of +9.
When loaded into hl, the engine will automatically play the textures as a repeated sequence going from 0 to 1 to 2 to 3 back to 0 (unless you go higher on the frames). Maximum frame is +9. I hope you understand how I explained it. The texture name must be the same on each frame, but the +X you should change depending on which frame you want that particular texture to be. So if I wanted to make a waterfall texture for example and I created five consecutive images mimicing the movement of water, I would then get the engine to flick between them by naming the textures like so:
+0waterfall
+1waterfall
+2waterfall
+3waterfall
+4waterfall
Then it would constantly flick between them in that sequence of 0,1,2,3,4 on the surfaces you've applied one of these texture to in hammer. Again, you need Wally to create your .wad files.
If I didn't explain something clearly or you still don't understand, then say so, but explain exactly what it is that you want or are having problems with.