Ever wonder how the water draining down your sink gets clean again? Think about it: The water you use to clean your dishes is the same water that runs through the toilet.  There is only one water pipe to the house, and that source provides water for the dishwasher, tub, sink, washing machine, toilet, fish tank, and water filter on the front of your fridge.  And there’s only one drain from your house, too!  How can you be sure what’s in the water you’re using?

This experiment will help you turn not only your coffee back into clear water, but the swamp muck from the back yard as well.  Let’s get started.
[am4show have=’p8;p9;p11;p38;p92;p80;p84;p101;p30;p57;’ guest_error=’Guest error message’ user_error=’User error message’ ]

  • clean play sand
  • alum (check the spice section of the grocery store)
  • distilled water
  • water sample (a cup of coffee with the ground put back in works great)
  • activated charcoal or carbon (check an aquarium store)
  • cheese cloth
  • clear disposable cups
  • popsicle sticks
  • medicine dropper or syringe (no needle)
  • funnel (the top portion of a water bottle can work also)
  • 2 cotton balls
  • measuring spoon (1/4 tsp and 1/2 tsp)


Download Student Worksheet & Exercises

There are several steps you need to understand as we go along:

  • Aeration:  Aerate water to release the trapped gas.  You do this in the experiment by pouring the water from one cup to another.
  • Coagulation: Alum collects small dirt particles, forming larger, sticky particles called floc.
  • Sedimentation: The larger floc particles settle to the bottom of the cup.
  • Filtration:  The smaller floc particles are trapped in the layer of sand and cotton.
  • Disinfection:  A small amount of disinfectant is added to kill the remaining bacteria.  This is for informational purposes only — we won’t be doing it in this experiment. (Bleach and kids don’t mix!)

Preparing the Sample

Make your “swamp muck” sample by filling a small pitcher with water, coffee, and the coffee grounds.  Fill up another small pitcher with clean water. In a third small pitcher, pour a small scoop of charcoal carbon and cold water.

Fill one clear plastic cup half full of swamp muck.  Stir in ½ teaspoon aluminum sulfate (also known as alum) and ¼ teaspoon calcium hydroxide (also known as lime; it’s nasty stuff to breathe in so keep it away from kids).  You have just made floc, the heavy stuff that settles to the bottom.

Aside: For pH balance, you can add small amounts of lime to raise the pH (level 7 is optimal), if you have pH indicators on hand (find these at the pharmacy).

Stir it up and sniff — then don’t touch for 10 minutes as you make the filter.

Making the Filter

Grab a cotton ball and fluff it out HUGE.  Then stuff it into the funnel.  The funnel will take two or three balls.  (Don’t stuff too hard, or nothing will get through!) Strain out the carbon granules from the pitcher, and put the black carbon water back into the pitcher.  Place the funnel over a clean cup and pour the black water directly over the cotton balls.  Run the dripped-out water back through the funnel a few times.  Those cotton balls will turn gray-black!  Discard all the carbon water.

Add a layer of sand over the top of the cotton balls. It should cover the balls entirely and come right up to the top of the funnel. Fill a third empty cup half-full of clean water from the pitcher.  Drip (using a dropper) clean water into the funnel. (This gets the filter saturated and ready to filter.)


It’s time to filter the swamp muck.  Without disturbing the sample, notice where the floc is… the dark, solid layer at the bottom.  You’ve already filtered out the larger particles without using a filter!  Using a dropper, take a sample from the layer above the floc (closer to the top of your container) and drip it into the funnel.  If you’ve set up your experiment just right, you’ll see clear water drip out of your funnel.

Continue this process until the liquid starts to turn pale – which indicates that your filter is saturated and can’t filter out any more particles.

To dissect the filter and find out where the muck got trapped, invert the funnel over four layers of paper towel.  Usually the blacker the cotton, the better the filter will work.  Look for coffee grounds in the sand.

“Radioactive” Sample

Activate a disposable light stick. Break open the light stick (use gloves when handling the inner liquid), and using the dropper, add the liquid to the funnel.  You can also drip the neon liquid by the drop into the swamp muck sample and pass it through your filter.

You can test out other types of “swamp muck” by mixing together other liquids (water, orange juice, etc.) and solids (citrus pulp, dirt, etc.).  Stay away from carrot juice, grape juice, and beets — they won’t work with this type of filter.


Have a question ?

Tell us what you're thinking...