Legionella are aerobic bacteria which appear naturally in all surface water and groundwater. From there despite water treatment and through raw water they can reach the drinking water systems and other water transporting installations. The invention LegiGuard is a fully automated minilab for the qualitative and quantitative determination of legionella in water pipes for e.g. drinking water. The device is able to take a defined volume of water from the water stream and to determine the existing amount of legionella. For this purpose fluorescently labeled immunobeads are used allowing easy detection of presence of legionella. The result is directly and electronically communicated to the user after 1.5 Â 2 hours.