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Filtration Fact Sheet - July 2009

Image of bottle filled with water.

Main Concept

Soils can filter and clean water. The ability of a soil to filter water is largely dependent upon particle size and how fast water flows through soil.

Educational Goals

  • Demonstrate how soils can clean water.

  • Understand what properties influence the filtering of water.

  • Understand how some chemicals that are spread on the ground can contaminate ground water.

  • Demonstrate that sand particles do not filter chemicals from water as well as silt and clay particles do.

  • Recognize that water flows through sandy soils faster than it does through clayey soils.

  • Predict the outcome if colored water flows through a loamy soil (a soil that contains a mixture of sand, silt, and clay).

Demonstration is suitable for kindergarten through college. Activity is designed for 5th – 8th Grade.

Materials & Preparation

√ 1 Stack of bottle filters filled with sandy soil
√ 1 Stack of bottle filters filled with clayey Soil
√ 1 Stack of bottle filters filled with Loamy Soil (Optional)
√ 1 Stand to secure bottle filters
√ 1 Gallon of Green colored water (Green will be used in this demonstration; food coloring recommended)
√ 1 Gradnated Measuring cup
√ 4-7 Clear plastic cups

 

Background

The relative proportions of sand, silt, clay, and organic matter influence how fast water moves through soil and how well water is cleaned. The longer it takes for water to flow through soil, the more time it has to interact with the soil and the cleaner the water becomes. Water moves slowly through clayey soils because the spaces between the individual clay particles are very small. Clay particles and organic matter have charges that attract some chemicals and keep them from moving through the soil. Water flows faster through sandy soils because of the large spaces between sand grains. The shorter time the water has to interact with the soil particles combined with the smaller surface area results in water that is not as clean as the water that flows through the clayey soil. The results of this experiment will vary over time based upon which holes the water passes through and how much water has been poured through the filters.

 

Explanation

If green water is poured quickly through a sandy soil, the water generally will end up green in the bottom bottle. If green water is poured very slowly through a soil high in silt and clay, it generally will take a long time to infiltrate into and through the soil, and the water will usually come out clear. If the soil is intermediate in texture, the water will come out light green.

Over time, a soil high in silt and clay will eventually become saturated with color. If green food coloring is used, light yellow water will make it through the soil first. Over time the water that makes it through the filter will gradually become more green.


> Go to Teacher Preparation Sheet
> Go to Student Exercises Sheet


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Download Printable Filtration Packet

A Printed Version of this Filtration packet is available in Adobe Acrobat.

Filtration Fact Sheet with Teacher Prep Sheet and Student Exercise
FiltrationFS_0709.pdf (PDF, 276 kb)