User search activities on the Web are getting more and more specialized: users expect more precise domain-specific results from search engines and typically perform complex tasks that involve exploratory, multi-step search processes. In this paper we propose the Liquid Query paradigm, that allows users finding responses to multi-domain queries through an exploratory information seeking approach, upon structured information collected from Web documents, deep Web data sources, and personal data repositories, wrapped by means of a uniform notion of search service. Liquid queries aim at filling the gap between generalized search systems, which are unable to find information spanning multiple topics, and domain-specific search systems, which cannot go beyond their domain limits. Liquid query provides a set of interaction primitives that let users make questions and explore results spanning over multiple sources, thus getting closer and closer to the sought information. We demonstrate our approach with a prototype built upon the YQL (Yahoo! Query Language) framework.