Shiva Purana
जलदेवान्नमस्कृत्य मंत्रेण स्नानमाचरेत् । अशक्तः कंठदघ्नं वा कटिदघ्नमथापि वा १६ ।
After making obeisance to the gods of water, the twice-born shall perform the ablution with mantras. Sick or weak persons shall take bath upto the neck or hips.
english translation
jaladevAnnamaskRtya maMtreNa snAnamAcaret । azaktaH kaMThadaghnaM vA kaTidaghnamathApi vA 16 ।
hk transliteration by Sanscript