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4-H Science Blast Activities: The Dirt on Clean Water


May 7, 2020 -

Educational Elements

Key Concept:

Soil as a water filtration system


The Dirt on Clean Water lesson plan is designed to assist leaders in teaching participants to understand that soil acts as a filter to keep pollutants out of our water supply. Participants divide into small groups to create filters to demonstrate and observe various soils as they act as water filters.

Age Level:

Ages 5 to 15 (Activities may be altered to fit a wide age span.)

Life Skills:

Critical thinking, problem solving, wise use of resources, responsible citizenship.

Success Indicators:

After completing this activity, participants will be able to: 

  • Identify the types of soil that best filter water. 
  • Use scientific process to determine the best type of soil for filtration. 
  • Be able to understand how pollutants affect the groundwater supply. 
  • Suggest ways to use soil as a natural filter in the outdoor environment.

Materials & Methods

Preparation Time: 15 minutes

Lesson Time: 45 minutes

Space: Classroom or outdoor space with tables


  • 3-ounce paper cups (one for each pair or group times the number of times they will filter water with different types of soil and soil combinations)
  • 5-ounce paper cups (one for each pair or group times the number of times they will filter water with different types of soil and soil combinations)
  • Toothpicks (one for each pair or group times the number of times they will filter water with different soil types and soil combinations)
  • Play sand (dried completely, in an oven if necessary) (It takes about ½ cup of soil or combinations of soil for each experiment run.)
  • Fine soil of one type or several different soil samples (dried completely, in an oven if necessary) (You can have participants bring soil samples from various sources such as their gardens or schoolyards.)
  • Water or access to water
  • Pitchers or water containers that can hold 1 quart of water (one for each pair or group)
  • Grape or other flavored nonsweetened drink mix (or green, red, or yellow food coloring)
  • “Floaties” (water contaminants such as small pieces of paper, dried grass clippings, small pieces of foam food containers, or other material)
  • “Recording Your Observations” worksheet (one for each participant) (For younger participants, recording may be done as a group.)
  • Writing utensils (one for each participant)


  • Aquifer – Areas underground where groundwater exists in sufficient quantities to supply wells or springs. 
  • Contaminant – A substance added to water that makes it unfit for use. 
  • Filtration – A mechanical process that involves moving water through a material, usually sand, designed to catch and remove particles. 
  • Groundwater – Water found under the ground, in aquifers and between soil particles. 
  • Infiltration – The gradual downward flow of water from the surface into the soil. 
  • Nonpoint source (NPS) Pollutants – Sediment, organic, and inorganic chemicals, and biological, radiological, and other toxic substances originating from land use activities, which are carried to lakes and streams as surface runoff and cause pollution. Nonpoint source pollution occurs when the rate of materials entering these waterbodies exceeds natural levels. 
  • Pollutant – Anything which alters the physical, chemical, or biological properties of water making it harmful or undesirable for use. 
  • Runoff – Precipitation that flows overland to surface streams, rivers and lakes.

Background Information:

Filtering water is one of soil’s most important functions. Soil can naturally filter out pollutants, such as fertilizers, gasoline, leaks from sewer pipes, and harmful bacteria from water. Through this process of naturally filtering many harmful toxins, the water is then safe as it enters our groundwater supply.

Most of our drinking water comes from aquifers. These are underground water sources that are “tapped,” which means wells are drilled through the soil and rock, and the water is pumped to the surface. Some communities store water in water towers once it is pumped up from the ground. People that do not live near a community water source drill private wells.

Gasoline, lawn care products, household cleaners, or other pollutants can contaminate the groundwater. These are known as nonpoint source pollutants, or NPS pollutants. These pollutants often enter the groundwater as runoff. Runoff usually happens when rainwater falls on impermeable surfaces such as roads, parking lots, or compacted soil. The runoff water picks up pollutants from these surfaces, and the pollutants enter the groundwater supply through rivers and streams. When water has the opportunity to move slowly through the soil, especially where there are plant roots, the toxins are filtered out of the water by binding to soil particles. The water is then naturally filtered and usable for drinking and other household purposes.


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