There are many reasons why dogs vomit water, such as:

Indigestion: Dogs eating inappropriate food or overeating may cause indigestion and vomit water.

Gastroenteritis: Infection or irritation of a dog's gastrointestinal tract may cause gastroenteritis, which may manifest as vomiting, diarrhea and other symptoms.

Gastrointestinal obstruction: Dogs accidentally eating foreign objects, such as bones, hair, etc., may cause gastrointestinal obstruction, resulting in vomiting.

Infectious diseases such as canine distemper and parvovirus: These diseases may also cause dogs to vomit water and other symptoms.

If a dog vomits water, the owner should closely observe the dog’s symptoms, take reasonable countermeasures, and seek professional veterinary help if necessary.