SubjectsFascinating FactsFactsIP FactoidsScience Facts Potassium can start a fire in water. By IP Factly - May 29, 2015 0 6 Share on Facebook Tweet on Twitter Image credit: peasap cc2.0 Potassium can ignite hydrogen in the air, which is why it can start fires. Water is also made up of hydrogen, too, though, so if you drop a small amount of powdered potassium in it, you’ll also be able to start a fire.