As water passes through the soil some compounds are held in the soil surface and others separate and may move quickly through the soil, leaching into the ground water. A black line drawn on filter paper and placed in water illustrates this principle. This illustration also works to explain capillary rise. For young students this is a simple demonstration of the primary colors as seen in a rainbow.

Nitrogen is a key nutrient in plant growth but all nitrogen compounds are not alike, one form is adsorbed while another leaches.  Using a simple test strip procedure, students will see if Nitrate, NO^-3, has leached through the soil and if it is found in various ground water samples.