I don't have an answer for you exactly (I would probably recommend just water to prevent any additional irritations, as you thought, unless someone can recommend a 'soothing' additive for the water).
The only point I wanted to make is: I have gone to a naturopath for about 9 years and have done all this stuff (fasting, colonics, flushes, juicing, parasite cleanses, etc. etc). My personal experience, when telling others what to try or not try, has come down to really encouraging them to go to a professional (I don't mean a regular MD!!, but a naturopath or similar alternative therapist) that can take certain readings to determine your body's readiness to even be trying some of the cleanses. In many, many instances, the body is not prepared fully for some of these detox treatments, and it could be you'd need specific vitamin/mineral assistance, you may need to be on a simplified diet first for a while, or any other number of things.
That recommendation is not intended to take away your ability to do your own healing, by any means! But, having someone direct you a bit, until you are better prepared (particularly since you had this quite negative side effect of trying a cleanse in the first place) would be well advised now.
Some things to have the alternative practitioner check for you is your body pH (through urine and saliva samples) called Rheams testing, and perhaps have them check your blood morphology which can identify yeast, parasites, and wheat intolerance, among other things.
Bodily weaknesses show up in these tests and are better predictors of whether you are ready to be doing some of the cleanses, or if you need some other preparation or support.
I haven't read your other posts, so if there is something I'm not informed about, please excuse the oversight.