A number of years ago our lab was asked by our Safety Department to check water samples from various water fountains for bacterial contamination and chlorine levels. We found many to be contaminated with a wide variety of bacteria. Upon examining the possible cause for the contamination we noted that water fountains that were not used on a regular basis (at least several times per day) had a significant degree of contamination and those with pre-filters (activated carbon within a fiberglass spun filter) had the highest level of bacterial contamination.

We attributed the findings to two observations:

Water fountains (at least ours) all have reservoir where the cooled water is stored and those water fountains with little use had, over time, become contaminated by backwash and since they were not being flushed regularly by use, the chlorine levels were zero and not being replaced by freshly chlorinated water. By having occupants flush these fountains daily, the bacterial contamination went to zero.

With the water fountains that had pre-filters installed, despite their regular use, the activated charcoal was removing the chlorine and once again, backwash was causing the contamination. The pre-filters were removed and bacterial contamination went to zero.

Pete