Doing them too frequently can kinda mess with your "regularity," but other than that, gentle plain water enemas are pretty safe. If it hurts, stop obviously.

OTOH, I have IBS (veering towards diarrhea most of the time), and find them pretty unpleasant. Pretty much any colonic stimulation (though I do like a little sphincter play now and again) makes me feel super queasy and pisses off my crabby guts.

But I second the recommendation for plain water. Your intestines just absorb pretty much anything straight into your bloodstream. If you wouldn't want it in an IV, don't put it in your butt.