On 22 June, pupils from all over the world helped to measure the pH (acidity) levels of local rivers and lakes. The results of the tests will help scientists to put together a huge online map of global water quality.

According to the Royal Society of Chemistry (RSC), it is the largest chemistry experiment ever carried out.

“We believe the results will provide a picture of global pH that will be very informative,” said the RSC President, Professor David Phillips. “So the work by students all over our country, and in others where the experiment took place on the same day, is of genuine national and international use.”

The pH levels of water are very important for aquatic plants and animals, as they are very sensitive to small changes in acidity. Acidic water can harm the gills of fish or even reduce the numbers of eggs that hatch. Heavy metals also dissolve more easily in acidic water, which can make water more toxic in polluted parts of the world.