Microplastics have been found in human brains, blood, placentas, and testes across 1,300 species. An 18-year-old in Virginia just built a filter in her garage that removes 95.5% of them. The physics of how it works is worth understanding. Traditional water filters use solid membranes. Water passes through, particles get caught. The problem: microplastics range from 5mm down to 1 micrometer. Filters fine enough to catch the smallest particles clog constantly and need replacing. The maintenance cost makes them impractical for household use. Mia Heller built exactly this, over and over, after water tests in Warrenton, Virginia showed PFAS and microplastic contamination. Government agencies said no public funds were coming. Residents were on their own. Heller took a completely different approach. Her system uses ferrofluid, a liquid containing magnetic nanoparticles suspended in oil. The key insight is polarity. Microplastics and water have different polarities. Microplastics are more attracted to the oily ferrofluid than they are to water. So when ferrofluid enters contaminated water, the microplastics migrate toward it on their own. Then you apply a magnetic field. The ferrofluid is magnetic. The magnet pulls the ferrofluid out of the water, and all the attached microplastics come with it. The ferrofluid is recovered and reused at an 87.15% recycling rate. No membrane. No clogging. No constant filter replacements. She went through five prototypes before getting it working. The system filters about a liter at a time and fits under a kitchen sink. She also built her own turbidity sensor to verify the removal rate, rather than relying on visual inspection. Municipal drinking water plants achieve 70 to 97% microplastic removal depending on technology. Her garage prototype hits 95.52%. She won a $500 prize at the Regeneron International Science and Engineering Fair for it. The constraint she already sees: ferrofluid is expensive to produce at scale. She designed the system for individual households, not treatment plants. But the mechanism, polarity and magnetism replacing physical filtration, is the kind of first-principles reasoning that makes the best engineering. Five prototypes. One garage. $500.