National Geographic : 1952 Aug
£ii B. LOUIS 'ose-lilSpaten, lIacK Star Turbid River Water in a Few Months Dumped This Muddy Mess into a St. Louis Basin On being purified, river water drops much of its mud in settling basins. Chemicals coagulate remaining sediment into jellylike masses. These are filtered by sand or crushed anthracite (page 283). Chlorine kills the bacteria. Thus in 24 hours a filter plant can turn murky, polluted water into the sparkling liquid we take for granted (inset). Before cities adopted filtering, mud might settle an eighth inch deep in a glass of tap water.