When it comes to purifying water contaminated by things like lead, heavy metals, and radiation, or using brackish or saltwater, boiling shouldn’t be your first resort. Instead, start by distilling the water.
The easiest way to do so is to use an oven-safe glass or cup and a large cooking pot. Place the smaller container in the center of your pot, with enough space for the lid to close.
Fill the pot with your contaminated water, being careful not to get any in the cup or glass, then set it to boil with the lid upside down. This allows the steam to run down the lid and drip into the smaller container.
You’ll need to keep a close eye on things throughout the process, as you don’t want to waste distilled water by letting the cup or glass overrun.
Carefully remove the pot from your heat source (or simply remove the lid) once the catcher is about 3-quarters full. Then, using heat-resistant protection for your hands, take the smaller container out and set it aside to cool.
This is a time-consuming process, especially considering how little water you’ll get. It also assumes you have all the necessary materials, including a stove or campfire.