Why do they call it a "dry enema?"

I recently learned that's the medical term for a rectal injection of water based lubricant, That describes the second low volume enema I give Carl every Sunday. She prefers about eight ounces of lube in the Sims position, which she immediately expels onto a towel without getting up. The expulsion is the perfect final prep for anal sex, but it's anything but “dry.” Hence my question.

The “dry” merely refers to the lack of water.

I don't think I would like a dry enema. I like that full feeling with four quarts.