You can do plain water, but it’s recommended you add 1 teaspoon of salt per quart of water to keep the salinity balanced with your body. You don’t want to introduce too much water to the system or, conversely, use too much salt. Always use clean, preferably filtered water, and ALWAYS check the temperature on your wrist to be certain it is close to your own temperature. The shock of very hot or very cold temperatures against the sensitive tissues inside you can actually cause serious damage!
HOWEVER, enemas can be uncomfortable and can flush out stuff from farther up the system, which can leave you less ‘clean’ than expected, or have you going to the bathroom over and over and just generally ruining the mood.
My recommendation if you want to be ‘clean’ in a quick, easy fashion: “dry enema” which involves simply inserting about 5-10cc of lube into your butt. You can accomplish this with a syringe (you can get one at a pharmacy, or find a lube shooter online). It’s super easy, usually works in under ten minutes, and actually leaves you a little lubed so you can play right away!