a bubbler at a melbourne high school has been dispensing recycled water .
students at st peter 's college in melbourne may have been drinking treated sewage water for around 16 months .
the horrific discovery was made by maintenance during school holidays .
investigation is under way by the department of health and human services .
students were at risk of contracting gastro while drinking from the bubbler .
the other 20 bubblers at the school have been tested and deemed safe .