One of the most important tasks at any water treatment plant is safeguarding the quality of drinking water. Worldwide, the drinking-water sector is increasingly aware of the limitations of end-product testing for ensuring safety. One limitation is the steady increase in the number of potentially occurring pathogens and chemicals that need to be monitored. A further limitation is the delayed availability of results in relation to the timing of interventions needed to maintain the safety of a supply. Ensuring the safety of a supply requires monitoring not only of the finished drinking-water, but particularly of parameters which indicate whether the key control measures in a given process are functioning correctly. Preventative measures have therefore become very important. The Hazard Analysis Critical Control Points system (HACCP) is a food safety management system which uses the approach of controlling critical points in food and drink production, and the framework of its concept consists of 7 principles. According to the Council Directive 93/43/EEC and the recent Regulation (EC) No 852/2004 on the hygiene of foodstuffs, the application of HACCP in food production is obligatory. In the present work, the HACCP principles were applied to the Aspropyrgos Water Treatment Plant. The critical control points identified include filtration and chemical disinfection.