Does the type of water you give a plant change how tall it grows? Each of these waters contains different dissolved substances. You can compare their effects on radish seeds. Set up three covered boxes with rock wool plugs. Place two radish seeds in each plug. Fill each box with one type of water so the rock wool absorbs it from below. Add an air pump and keep all boxes the same distance from a light source. Measure the height of each plant twice a week for three weeks. Weigh the plants at the end. In one trial, seltzer water produced the tallest plants and the most germinated seeds. Mineral water produced the heaviest plants. Tap water had the weakest growth overall.