This study is a reflection about applications of stable water isotopes as a hydrologic tracer in Schelde Basin water management.The Schelde Basin is a low land river system that extends from northern France through northern Belgium to the most southern part of the Netherlands. The Schelde Basin is densely populated and hosts vast industrial and agricultural activity, which leads to high levels of pollution due to a lack of complete wastewater and sewage treatment, and to agricultural practices. Land reclamation strongly reduced the river valley and intertidal zone, thereby reducing the natural storage capacity of the river, which creates serious flood safety problems.Decision-makers are increasingly convinced of the necessity to consider ecological quality, economy and safety as part of the same integrated management. A first step in decision-making is well understanding the problem (Meire et al, 1997).We are convinced that stable water isotope methods can contribute to this.A survey was made of the variations in precipitation, groundwater, river and estuarine water, and seawater, although the gravity center was the estuarine zone of the Zeeschelde. 1230 different samples were analyzed for dO and about 100 for dD. The used C02-equilibration method for stable oxygen isotope analysis (after Epstein et al., 1953) is characterized by a standard deviation of 0,12 ‰. The zinc reduction method (after Coleman et al., 1982) was used for deuterium analysis (standard deviation of 1 ‰).