CPV code 50411100 designates Repair and maintenance services of water meters in the Common Procurement Vocabulary (CPV 2008), the EU classification used to describe the subject of public contracts.
50411100 is a leaf code — the most specific level of its branch — so it can be used directly as the main CPV code of a contract notice. If it does not quite fit, check the neighbouring codes under 50411000 (Repair and maintenance services of measuring apparatus).