I cap the measured temperature of enema water solutions to 105 degrees F (40.5 degrees F) as measured with a calibrated thermometer. A minimum of two recent vintage calibrated thermometers are kept in the home with one used to cross check the measurement of the other. Beware of bargain priced 'clinical thermometers' and always calibrate against a known good thermometer across the temperature range you are measuring.
It is interesting to note that a website sponsored by a plumbing business states that a temperature of 110 degrees F is generally considered safe but that the human pain threshold is documented to be around 106 - 108 degrees F. ( https://1800anytyme.com/blog/how-water-how-hot-is-too-hot/ )
While some of the below references indicate 110 F (43.3 C) is a safe upper limit I err on the side of safety. My experience has been water administered at 38.7C to 40.5 C (measured) minimizes cramping, produces a thorough evacuation and minimizes incident of post enema leakage due to residual enema fluid. The time interval between completion of preparation of the enema ready for use and start time of administration is three to four minutes, thus thermal losses further lower the solution temperature before actual use.
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The recommendations below were gleaned from articles written by professionals in medicine:
https://www.registerednursern.com/how-to-give-an-enema-enema-administration-clinical-nursing-skills/
3. Warm the solution before placing it into an enema bag or bulb to a temperature between 99 and 106 degrees. (Note the temperature is in Fahrenheit units.)
https://www.nursingtimes.net/clinical-archive/gastroenterology/how-to-administer-an-enema-16-05-2006/
Dougherty and Lister (2004) recommend a solution temperature of 40.5-43.3 degs C for non-oil-based enemas. Cold solutions should be avoided as they may cause cramping.
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Other professional sites suggested 'Lukewarm" and "Room Temperature" were the optimal temperature choice for enema solutions.
A quick Google search indicates that the definition of "Lukewarm" varies. Two seemingly dominant definitions indicate that the temperature ranges for "Lukewarm" are 100 F - 110 F ( 37.8 C - 43.3 C) and 98 F - 105 F ( 36.7 C - 40.6 C).
Room Temperature definitions noted almost universally listed 68 F or the range 68 F - 72 F as Room Temperature.
Information on what an appropriate temperature for enema solutions is seems to not be cast in concrete in my opinion. Many sites offering advice on enema administration are vague at best on what temperature is appropriate.
Be careful.