Drinking water quality after flooding and torrential rains

In the event of heavy rain or even flooding, it can always happen that the drinking water quality is locally impaired and drinking should be avoided. In extreme cases, the sewage system can overflow, releasing various pollutants.

Bacteria and nitrates, which, for example, are spread on the fields with the liquid manure, or other pollutants can be washed from the surface into water bodies or groundwater and then cause problems in the water supply weeks or even months later and exceed limit values. Often a delay of a month can be observed between a heavy rainfall and the detection of elevated levels of pathogens in rivers and lakes, and up to two months before they are found in groundwater.

However, it is not only pathogens or other natural contaminants, but also pesticides and herbicides that are transported in increased quantities during such events.

A global study examined extreme weather events between 1910 and 2010, and found that heavy rain and flooding were the most common events that preceded outbreaks of waterborne diseases. More than half of these outbreaks were caused by contaminated drinking water.
(Cann KF, Thomas DR, Salmon RL, et al. Extreme water-related weather events and waterborne disease. Epidemiology and Infection. (2013). 131: 671-686)

In this country, gastrointestinal diseases are usually the result, but Legionella can also cause problems. In certain areas there may also be elevated levels of heavy metals after floods or heavy rain. Professional water analyses for legionella, bacteria and/or heavy metals can be found here.