How does reverse osmosis actually work?

Reverse osmosis isn't just a fancy water purification method—it's a powerful but double-edged tool that forces water through a semi-permeable membrane under pressure, removing contaminants like PFAS and salt. But here's the catch: it strips out not just harmful substances, but also essential minerals like calcium and magnesium that are good for your health. Without remineralization, the resulting water becomes so pure it can leach metals from pipes, potentially worsening contamination. A shocking study found that water from popular kiosks using reverse osmosis had higher lead levels than regulated tap water—because the unregulated systems didn’t test for metals, only PFAS. Meanwhile, a quirky kitchen hack involving aluminum foil in dishwashers may actually work through a redox reaction or galvanic corrosion, where aluminum sacrifices itself to protect stainless steel, though the exact mechanism remains a fascinating chemistry mystery. And in pharmaceuticals, the 'Brazil nut effect' explains why larger particles rise to the top when powders are vibrated—critical for ensuring medicine batches are evenly mixed. These everyday phenomena reveal how deeply chemistry shapes our lives, from clean water to clean dishes to reliable pills.