Cats vomiting hair balls and yellow water may be caused by hair balls, gastrointestinal diseases or viral infections. You need to pay attention to the state of your cat. If you have symptoms such as poor energy, loss of appetite, diarrhea, etc., it is best to treat it immediately. Send the cat to the pet hospital for examination and treatment. If there are no other abnormalities, you can feed the cat some cat grass and hair removal cream to help relieve the symptoms.