I scanned through Uny's post on the high enema instructions and found this:
"Remember, you'll likely be assimilating a LOT of plain/empty water into your bloodstream (which can imbalance electrolytes temporarily); using a solution of a weak herbal tea would be very beneficial (particularly an herb like comfrey leaf that's ultra-high in minerals/nutrients)."
But...she is talking about doing a High enema, consisting of a quart or two of water..(edit* Uny says 2-4 quarts, my bad:) You are doing them one litre at a time, so I'd assume that it wouldn't drain too much of your minerals (anyone else who may know differently please correct me!). Are you taking superfood at all? I know this would be very helpful in replenishing minerals, as would fresh juices- celery, cucumber, greens, etc.
That being said, are you filtering this tap water first before using it in a enema? This is imperative, as your colon will absorb those nasty tap water toxins!