Why is my stool always watery?

Not normal. Lots of causes including parasites, infection, inflammation of large or small bowel, overgrowth of bacteria in small bowel, colon, meds, rarely tumors;other causes needs to be checked by md; go see one.
Watery Stools. Also, do not take an anti-diarrheal medications (ex. Immodium) until you see a doctor first. This can seriously make matters worse! follow dr. Heller's advice to a tee.