Not all purification methods remove the same contaminants. Distillation heats water into steam and collects it, leaving most dissolved chemicals and bacteria behind. Filtration pushes water through a barrier that traps particles. Solar pasteurization uses sunlight to heat water enough to kill germs — but it does not remove dissolved chemicals. When you test all three against tap water, Chicago River water, and E. coli B bacteria across eight contaminants, the differences become clear: distillation removes the most and kills the most bacteria, filtration is fastest and cheapest, and solar pasteurization ranks last in three of four categories.

Purification often works in stages, where each step catches what the last one missed. Pouring dirty water through a strainer removes the largest particles. Letting that water settle in a tube lets fine particles sink to the bottom. Then comes the layered filter — charcoal, sand, and gravel packed together. Each material grabs different-sized bits of dirt, so stacking them removes more contamination than any single material alone. The layered filter does the heaviest work, trapping tiny particles that the strainer and settling missed.