There are two files, the package is the in game terrain paint, the DDS file is for use with CAW. Put it in your My Documents >> Electronic Arts >> The Sims 3 Create a World Tool >> UserToolData >> SourceTextures. I didn't test in CAW, however, it should work the same. It may take a bit of playing with to get your pond shape ideal, the image is lily pad heavy. If I do another, I may go with more water, less lily. I was afraid of how the water would look, but it came out looking pretty good. I hope you can make some good use of this, I will be adding the CAW file to the Rejected Repository list for CAW resources. I'll soon be moving all those files to the one folder in my Mediafire, rather than hosted on the Wiki, as there is limited attachments there.
Download - Terrain Paint
Download - CAW Resource