hello sgpierce,
                      watery diarrhea cause by -viral infection,salmonella,shigella,campylobactoer,cholera, some time crohn's disease-advice- hospitalization immediately- iv fluid -ringer lactate , to cover 
dehydration, antibiotic,symatomatic,& ORS solution drink,avoid milk product & tea &coffee, imodium (
loperamide)-  it s not proper medicine for diarrhea, side effect-
constipation, 
paralytic ileus,abdominal  distension,pain bloting,nausea, vomiting, dizzness &rash, in diet- avoid- oily,spicey food, hope my advice is useful to you, thank you.