Enterococci are a normally-occurring bacteria type which is usually found in the human gut and/or bowel, as well as the female genitourinary tract. When within the human body in this capacity, enterococci have little effect and carriers run minimal risk of any infection. Enterococci can become a problem, however, when it finds its way into the blood, wounds or urine of an individual. As with other types of bacteria, healthy individuals are often not affected but people with more vulnerable health statuses are more susceptible. Results of infection by enterococci include urinary tract infections, diverticulitis and meningitis.
As is the case with other bacteria where the usual environment is the gastrointestinal tract of humans and other mammals, enterococci's presence in drinking water is an indicator that faecal contamination has occurred and that the quality of the drinking water has been compromised. Under the Private Water Supplies Regulations, the presence of any enterococci in a tested water sample constitutes a test failure, and the recommendation is not to drink the water coming straight from the tap until effective treatment has taken place.