It may be spelt that way in your neck of the woods, there is normally plenty of it about, but in the home of the language it's;

OXFORD ENGLISH DICTIONARY:

diarrhoea

/diree/ (US diarrhea)

noun a condition in which faeces are discharged from the bowels frequently and in a liquid form.

DERIVATIVES diarrhoeal adjective diarrhoeic adjective.

ORIGIN Greek diarrhoia, from diarrhein flow through.

So, straight from the horses mouth as they say, (no pun intended)