The Efke 25 is pretty good in my experience and you can certainly get some nicely blurred water with it. The emulsion is mildly soft; some people have problems with scratched film. I've never had a problem.
You may also consider looking into Efke's positive paper. It's a photo paper that processes as a direct positive print (there is no negative, you make a print in the camera). It has an ISO of about 2.
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Efke 25
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Efke Positive Paper