CPV code 90713100 designates Consulting services for water-supply and waste-water other than for construction in the Common Procurement Vocabulary (CPV 2008), the EU classification used to describe the subject of public contracts.
90713100 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 90713000 (Environmental issues consultancy services).