A childhood belief about water

At my school, when you went out to recess you would play on a large asphalt lot that had a drain at one end so that puddles wouldn't form on the play area when it rained. When I was in first grade my friend and I were absolutely convinced that this drain was the source of all the city's water supply. We had noticed that when it rained the water going down the drain usually had mud or leaves in it, or gasoline that had dripped from cars. We couldn't beleive that the mayor would let people drink this water! So my friend and I, feeling an obligation to our community, got together a bunch of kids to build a "dam" around the drain. We built it of rocks and twigs, and assumed that it would hold out all the water that had been sitting on the dirty asphalt while still letting in rainwater. When we went away to got more rocks some older kids came and stomped on our dam, letting all the water in (of course our little dam hadn't realy held out any water anyway). For days afterward we would not drink any tap water.