I use tap water, but one has to make sure the water in your area is safe. Generally, what seems to me to be logical, is if you can drink it (water) it's OK for an enema. I certainly don't claim to be an expert at all, but that's what I've done over the years. I do enemas in the shower, just because of my living situation it's easier and I can have some fun. I have a very smooth shower hose, so I just stick it up my asshole and use how hard I squeeze my ass cheeks to determine the pressure. Also, I can let it go in the shower and for the most part it's a pretty easy clean up.
Here is a word of caution, I've heard using too many plain water enemas at once can be harmful because one can offset the electrolyte balance in their body, something like that. This is a great forum to explore questions like that, there are many real experts in this forum on very safe enemas. I've been doing them a long time, I was just describing what works for me, I've always lived in very safe water areas.
However, I was once in London and did a large enema with tap water. The shower had a very very very long hose for some reason and I just could not resist laying down across the shower and shoving the hose up my asshole. That day I was really relaxed, I took a huge one. Later that day, about an hour later, I was out for a luncheon and suddenly felt very faint, then it passed. I've often wondered if I should not have done that. The rest of my stay there for several weeks I did not do another enema that way.
Ha, then in Germany once, I did a large shower enema and of all things I plugged the shower drain in the small hotel I was staying at. I freaked out some thinking what am I going to tell them. Then, luckily, I noticed there was an easy clean out trap by the shower, I lifted it and all was OK. Phew!!!!