Daniel BuenoThe bacteria in a drop of water stick to the part of the body where they fall. For example, if a drop from a marquee falls on the elbow, the bacteria will not migrate to the hand. Besides, it is very unusual for a single drop of dirty water to lead to health problems.
The skin is an excellent defense system. When it is in perfect condition, with no lesions or cuts, a dirty drop will cause no problems at all; the bacteria are unable to invade our body and they die. In this case, washing that body part with soap and water is enough to avoid health problems.
In other circumstances, such as crossing a torrent or flooded area, the bacteria in the water can cause infections of the skin itself or of other body parts by entering the body via a wound.
Leptospirosis is one such example. The bacteria that cause the disease come from rat urine and they can remain in water. When one has contact with this contaminated water, skin wounds can make it easier for the bacteria of the Leptospira genus to enter the organism. In general, however, even in such cases, undamaged skin is usually able to keep one safe from disease.
Senior professor of Infectology at the Department of Medicine of the Paulista Medical School of Unifesp