A tiny device that instantly determines if water is safe to drink just by analyzing the electric field around it — no strips, no microfluidics, no toxic chemicals. The whole thing is based on the electromagnetic fields that surround everything. Water creates its own local field, which is measured by moving the TestDrop through it, and it turns out that clean water emits a slightly different field than water with lead or chlorine in it, water with E. coli, water with dissolved animal matter and so on. The replaceable watch battery should last for years even if you’re using the device 10 or 20 times a day.