Discover the rocks that absorb water the fastest. Choose five to 10 different-looking rocks that fit into the same-size disposable cups. Pour 4 to 8 ounces of water over each one. Leave them alone for 24 hours. On the next day, carefully lift each rock out and measure the water again to see how much is left. Write down the amount that remains for each rock. The one with the least water left is the most porous. Measure the lengths and widths to determine if they changed in size. Be aware that very porous rocks may disintegrate inside the cup of water.
Choose several different types of rocks and look at them carefully. If possible, examine them under a microscope and document if there are cracks. Next, place them in water for 24 hours to give them time to absorb. Remove them from the water and put each one in the freezer for another 24 hours. Take the rocks out of the freezer and examine them again under your microscope. Since water expands when frozen, check to see if there is damage to any of the rocks or if some have broken apart.
Look for rocks that have different characteristics. Put them in a cloth bag, and use a hammer to carefully tap the outside of the bag and break the rocks in half. If they shatter, use a piece that is at least 1 square inch with a flat surface. Line up different rock pieces with the broken side on top. Using a dropper, put three drops of water on the surface of every rock and record how fast the water is absorbed by each one. The rocks that are not as porous as others may either absorb at a slower rate or not at all. Leave the rocks there overnight and record your final findings the next day.
Obtain rocks about the same size from digging in moist soil. Wash the rocks off outside and dry them with a paper towels. Place each rock in a disposable cup and cover with plastic wrap secured with a rubber band around the top rim of the cup. Let the rocks sit undisturbed in a warm area for 24 hours. Look for condensation on the plastic wrap due to the moisture inside the rocks. If you don't find condensation, leave them there for one more day. Remove the plastic wrap and drain the water on it and in the cup into a device that measures small amount of liquids to tell which rock holds the most water.