Whether you’re planning a camping trip or anticipating a power outage, you can never be too prepared when it comes to your flashlight stash. Batteries are bulky, expensive, and risk polluting the environment with harmful chemicals when improperly disposed of. This DIY water-powered flashlight, however, uses an energy source that’s safe and free.

Instructables user ASCAS published his step-by-step instructions online for creating an H2O-fueled flashlight out of PVC pipe and a special battery. The most important step is constructing the galvanic cell for the flashlight's core. This type of battery works through a salt bridge connecting two different metals (in this case, zinc and copper). It’s the same basic principle behind how a store-bought battery works, but in this case water is the electrolyte that powers it. It produces a pretty weak voltage, so the flashlight calls for the construction of a “Joule Thief Circuit” that’s capable of stretching the life out of faint batteries to power an LED. Some other materials include a general purpose NPN transistor, 1K Ohm resistor, copper wire, and tissue paper (things you should have no trouble finding at a hardware store, electronics store, or at home). The final product runs for 30 continuous minutes with tap water and up to 2 hours with saltwater. According to ASCAS, the ideal fuel is vinegar and Gatorade which are both rich in electrolytes.

While it does require water to function, it would be more accurate to say the flashlight is powered by its galvanic cell. The purpose of using water as the battery’s electrolyte is that it removes the need for heavy metals like lead and mercury that are often seen in conventional batteries. It also means you don’t have to pack batteries on your next camping trip as long as there’s a stream or other water source nearby. You can check out the full instructions on Instructables.com.

Banner image courtesy of Tech Builder via YouTube.

[h/t: Instructables]