While boiling water is generally the best way to purify it, this won’t work for water pulled from a hot tub or swimming pool. Boiling won’t remove the chemicals present in the water. Thus, you’ll want to know how to easily distill water.
You’ll need a large pot with a lid, a large heatproof cup or mug, and string. Fill the pot 1/3 to 1/2 with water from the pool. After making sure the top of the lid is clean, turn it upside down and tie the cup to the lid in such a way that the cup will remain upright while suspended from the string. Place the upside down lid over the pot and make sure the cup doesn’t go into the water. If the string is too long, adjust it accordingly.
The lid should fit tightly on the pot, leaving no gaps. Bring the water in the pot to a boil, then remove it from the heat. Do not remove the lid from the pot until the pot is cooled down.
What will happen is the steam from the boiling water will condense on the lid and drip into the cup. Naturally, you’re not going to be able to distill great quantities of water at one time using this method. But if you’re only source of water is either from the ocean (saltwater) or from a swimming pool that has been treated with chemicals, distilling it will make it potable.