How to Keep Leaching from Polluting Water Sources?

Author: Janice VanCleave

What You Need to Know

Potable water is water that is safe to drink. The downward flow of water through the spaces that are in soil is called percolation. Runoff is water that does not get absorbed by the soil; instead, it flows across the ground. Nitrate is a type of chemical substance that contains nitrogen, which is necessary for plant growth. Leaching is the process by which nutrients in soil are dissolved in water and carried away. Groundwater is water that is found below the ground surface.

How Does Leaching Work?

When the spaces between soil particles become filled with water, gravity pulls the water down through the soil. This is called percolation. The water that is not absorbed by the soil runs across its surface, and is called runoff. In both methods of water movement, chemical substances in the soil, such as nitrates, dissolve in the water and are carried away. This movement of water and dissolved materials is called leaching.

Fun Fact

In tropical rain forests, very little nutrients accumulate in the soil. This is because they are quickly absorbed by plants or leached away by rain. Because the soil of tropical rain forests is so nutrient- poor, areas that are cleared for growing crops (plants grown for food) are soon not very productive.

How Does Leaching Work?

What Does This Have to Do with Chemicals Polluting Water Sources?

Chemical substances, such as fertilizers and pesticides, leached out of the soil due to percolation can mix with and pollute groundwater. Chemical substances leached out of the soil by runoff can drain into rivers, lakes, or streams and pollute the water.

Real-Life Science Challenge

In areas where nitrates tend to be leached from the soil, other forms of nitrogen fertilizers, such as ammonium, can be used. Unlike nitrate, ammonium tends to attach to the soil particles and resists being leached by moving water.


Now, start experimenting with ways to keep leaching from polluting water sources.


  • Food coloring can be used to represent chemicals in the soil.
  • Does the type of soil affect the amount of leaching?
  • How do different plants affect leaching?
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