Water filter idea | Emergency Preparedness | Forums

my wife and I went christmas shopping the other day and we were walking through the sporting goods store when I walked by a igloo water cooler display

right then I had a epiphany of making it into a self contained water filter, put in a bed of stones on the bottom, then some smaller aggregate and the top 2/3rds filled with sand, basically make a mini slow sand filter, pour dirty water into the top and have clean water come out the bottom, I would still probably boil further because it wouldn't have time to build up the bacteria layer that is key to a slow sand filter. Thoughts?