Cleaning Dirty Water

Last week we mixed water and soil.  Today we decided to clean the water using filters.  We were allowed to select from the following items:  cloth, cotton wool, coffee filters, stones, sand.  We made these into a filter and put the dirty water in.  Our most successful filter was the cotton wool filter. We know that waste toilet water gets filtered, and so does waste waster on the International Space Station.  We enjoyed making our own decisions when carrying out this investigation.