Pupils from British schools participated in the world's biggest-ever chemistry experiment last Wednesday, aiming to provide a picture of the planet's pH levels. The experiment was the largest single collection of data on water quality ever undertaken at one time. Pupils visited local rivers, lakes and waterways to check acidity and their results will later form part of a highly valuable report on the quality of the world's water. By conducting the pH tests, students will contribute to an online global "map" of water quality and treatment. The Global Water Experiment was the centrepiece of the International Year of Chemistry 2011.