From “Holy Springs and Holy Water: Underestimated Sources of Illness?” published last year in the Journal of Water and Health.
Holy water is used throughout life in Catholic ceremonies, holy springs visited for pilgrimage or in cases of illness. Holy water is made at Easter, when tap water is blessed and stored. Our study investigated a variety of holy springs and holy waters in Lower Austria and Burgenland. At each sampling, a sanitary inspection was performed. Odor and appearance were checked on-site. The taste of the water was not assessed. During sampling, we observed people filling up several bottles of water, and parents trying to persuade children of the high quality of the water.
A high percentage of samples was contaminated with fecal indicator bacteria: 76 percent with coliform bacteria, 38 percent with E. coli, and 32 percent with enterococci. Less frequently visited churches were much less contaminated, indicating that dipping of fingers is the main reason for microbial growth — bacteria from the skin are transferred into the water and nutrients for growth arrive in the font.
To prevent people from using these waters, clear warning signs have to be installed stating that springs are not suitable for drinking. An even better solution would be a light sensor that dispenses water from a small tank by putting a hand under it. For hospital chapels where injured or immunosuppressed patients have access, it may be wise to completely avoid the use of holy water.