Building a decentralised water information portal based on the aggregation of national water information systems is a promising solution in terms of flexibility, system sustainability (commitment from developing countries) and responsiveness to end-users needs. In this domain, the Euro-Mediterranean Information System on Know-How in the Water Sector (EMWIS) is bringing significant experience at organisational and technical levels. Today, Internet technologies and associated standards offer unique opportunities to build in such flexible integrated systems able to collect dynamically information from peer systems. International efforts should concentrate on communication protocols and information structures to efficiently use and share water information and build new knowledge. Water information is a cornerstone, necessary to build new cooperation initiatives, to monitor and assess projects achievements, to build efficient dialogue among stakeholders, to ensure public awareness and for planning and decision making. Its importance has widely been recognised at the highest political level. Web services are based on the extensible mark-up language (XML) also used to develop the so-called "semantic Web". EMWIS is exploring the development of a specific XML grammar (Water-ML) to insure the interoperability of water information systems developed in various part of the world. To complete this specific grammar and repository of water information services, water ontology is being developed. It make searches easier and more accurate for the end-user.