Safe drinking water is essential for human health and sustainable development. In the last ( ) 30 years, the International Development Research Centre IDRC has funded over 200 applied research projects on tools and strategies for improving water and sanitation conditions in poor populations around the world. Realizing that the safety of drinking water is just as dependent on being toxicant free as on being pathogen free, the IDRC initiated WaterTox, a novel international research network with scientific institutions from Argentina, Canada, Chile, Colombia, Costa Rica, India, Mexico, and the Ukraine. The objectives of WaterTox were to develop and validate a battery of simple, inexpensive and practical bioassays for toxicity testing of water samples, to identify and validate appropriate sample concentration alternatives that would allow the battery of bioassays to assess the potential toxicity of waters used for human consumption, and to design, in collaboration with network partners, a strategy to promote the adoption of this battery for toxicity testing at the international level. The bioassays selected for WaterTox were based on the premise that they should be able to be performed in-country without the need for expensive imported supplies. A description of the procedures to establish the WaterTox project, the laboratories involved, the problems encountered, and results obtained are presented in this overview report.