I get it actually, but droning sounds actually irritate me and make me tense. So the water running will sound good for a few minutes but then aggravate me.
I prefer underwater sounds. There tends to be a natural slight drone but it's less obvious and usually a deeper sound making it easier to handle. And if turned down you may not hear it at all but still hear the motion of the water.
Some of the "space ship" sounds aren't too bad. Depends on my mood.