Ok I don't know if I'm gonna sound dumb, but I am doing my 6th grade science experiement and i need to know what the control is. I am going to test tap, bottled, fountain, and toilet water. I want to see which one has more bacteria and which is more drinkable, i read somewhere that toilet water is just about the same as fountain i want to know. Can somoen tell me what the control is because i cant figure it out

A control in an experiment is a sample you do as a "baseline" to give you an idea of what "normal" might be. So if I were testing to see if adding dirt makes water have more bacteria, I'd have a bottle of clean water and one of dirty water and test both of them. The clean water would be the "control."

 

So make one of your water sources the "control", what you'd call "normal" water. You can then compare all of your other tests to it and see if they have more or less bacteria than "normal" water.

Thanx very much.

Your control should probably be distilled water that is boiled immediately before testing to make sure there are no bacteria living in it. If you are going to be growing cultures of each, absolutely nothing should grow on that sample.

 

You may get very few results, since tap water (which ends up in your sinks, water fountains, and toilets) is usually chlorinated which will kill most bacteria. Be prepared to explain your results if every sample ends up with none or very little in the way of bacteria.

 

As a side comparison, you may also want to test the toilet seat/rim, top surface of the water fountain, kitchen sink, outside of a water bottle, which are also useful indicators of cleanliness of certain water sources.

 

More repetitions make your results more credible, so I would take samples from a few different toilets, water fountains, sinks, etc. and present your results as averages.

Edited February 3, 200916 yr by UC