If you haven’t used your tap for a long time, for example after a holiday, you should let it run first to let the stagnant water drain away. The reason: bacteria such as legionella may have accumulated in the water pipes. Especially when it is warm in this country, because legionella multiply at a temperature between 25 and 55 degrees Celsius. Infection usually does not occur through drinking, but through the aerosols that can get into the respiratory tract when using the tap or shower. Legionella infection can be dangerous, but it doesn’t have to be. A severe infection threatens a dangerous pneumonia, in milder cases an infection leads to the less dangerous Pontiac fever. This usually goes away on its own. Tip: If you have friends or family who look after your house during your vacation time, they can do something to prevent the bacteria from multiplying. For this, water should be bottled at a tap that is far from the main water supply. In a family home, this is usually the upper bathroom. This keeps the water moving in a large area of the supply lines.