Many infectious agents can be spread through water and cause illness in people who ingest contaminated water. Water contaminated by bacteria and viruses mainly causes gastric and intestinal infections. Exposure can occur through ingestion of drinking water, but you can also be exposed via, for example, bathing water and vegetables irrigated with contaminated water. Aerosols from, for example, showers can contain legionella which, if inhaled, can cause severe pneumonia.
Drinking water intended for general consumption is produced and controlled in accordance with the requirements of the Drinking Water Regulation. It is the responsibility of the water producer to provide drinking water which, according to the legislation, must be "healthy and clean" and meet quality requirements. Only in exceptional cases is the drinking water in Sweden contaminated with pathogenic microorganisms (pathogens, hereinafter referred to as infectious agents) and can therefore cause health problems.
In the production of drinking water, surface water from lakes and streams or groundwater is used. These so-called raw waters can be contaminated in various ways and if the treatment in the water plant is not sufficient to kill the infectious agents, these can spread further to consumers. Drinking water can also be contaminated in the pipe network during transport from the aqueduct to the tap. Individual wells can be contaminated and then present a risk because they rarely have a system for purifying microorganisms.
It is mainly stomach and intestinal infections that are caused by contaminated drinking water. Symptoms and incubation period depend on the infectious agent that has entered the drinking water system. If drinking water is affected by sewage, it can lead to the spread of various infectious agents.
Only a small part of the cases of diseases caused by water are known. In the case of gastric and intestinal symptoms, the cause is rarely known and only in exceptional cases does the affected person consult a doctor. It is especially during several cases in a family having its own well, or during epidemics where a greater number of people fall sick at a close time, that one discovers that drinking water is the cause.