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Your results might not be exactly the same as ours, but they should be similar.

Our “contaminated” water samples were an unappealing green color from the food coloring we used. We observed that our samples were sort of cloudy, with a layer of oil on the top, and some soil and fine sand were on the bottom. There was also a vanilla smell.

After we stirred the alum into container 1 and let it sit for 15 minutes, we observed that there was some clumping and settling of particles. The color appeared to be slightly lighter.

It took about three hours for the samples to drain through the filters. Once all the water passed through the gravel and sand, the samples looked very different from when they were poured into the filters.

The second photo shows that both filtered samples are lighter in color than when they were poured in. However, water sample 1, which contained the alum, is much clearer and lighter in color than sample 2. We could no longer detect any vanilla smell in either sample.

We conclude that the filtering system was effective in removing some of the “contaminants” from both water samples and that the alum treatment was more effective than sand and gravel alone.

We added two drops of hydrogen peroxide to filtered sample 1 but did not notice a significant difference. It is possible that this helped to make the water even clearer, but we are not sure. Your results might show a more definite change.

The alum and hydrogen peroxide represent typical chemical treatments, while the settling and the sand-and-gravel filter represent typical physical treatments that might be found in large-scale water treatment plants. The actual treatments in water plants are similar. The treatments in this activity are for demonstration purposes only and are not intended to produce purified drinking water.