Knowing how water passes through soil is very important. For example, engineers need to know how quickly water will drain away from buildings or bridges. Drainage rates are also important to farmers, landscapers, gardeners, environmental scientists, and other professionals. Water is one chemical found in soil. There are many others. Some of the chemicals in soil are very important for plant growth. Farmers and gardeners often test their soil for these chemicals using soil-testing kits. These kits can be bought at gardening or hardware stores.