If your poop only comes out like water for a short time and returns to normal after a day or so then it's most likely just Diarrhea that will correct itself after awhile.
If your poop is constantly coming out as liquid then it could be a problem with your bowels such as Crohn's disease or or even ulcerative colitis.
It's a disease of the intestines and if the watery poop doesn't stop after a few days then you should see a doctor about it so they can do some tests to find out what the exact problem is and correct the problem.
Your bowels or intestines could be infected by some bacteria as well.