known issue, currently we are working over the general improvement of the splash generation and shading. if this is important for you, may ask for nightly build access and to try with the latest changes.
for now i would recommend to render the splash with motion blur, it hides the lines a lot. see this test
Thanks Ivaylo, I have the motion blur currently on. Which does coverup some parts a bit but it is visible in bigger chunks since they all have similar velocity. But I will try the nightly build changes