In general there is no harm in washing the buttocks with tap water, but if there is a wound on the buttocks, washing with tap water may cause infection. Human skin covers the surface of the body and is in direct contact with the external environment and can serve functions such as protection and barrier. A normal person, if the skin on the buttocks is intact, the barrier and protection of the function is not destroyed, normal cleaning does not have any harm, are within the tolerance of the skin. Moreover, washing the buttocks can have a cleansing effect. Therefore, if there is no broken skin on the buttocks, you can wash the buttocks with tap water to clean the anus. If there is skin breakage or trauma, etc., you should not use tap water to clean it. Tap water still contains bacteria, and the barrier and protective function of the damaged skin is greatly reduced, so rinsing with tap water may cause or aggravate the infection. You can use sterile saline, or 1:5000 potassium permanganate solution to wash or sitz bath.