In 2011, two people in Louisiana died from brain infections linked to the amoeba Naegleria fowleri, found in local tap water. Stomach acid kills this pathogen when people drink the water, but neti pot use or swimming in unprocessed water puts the critters inside your head.
What makes the difference, and what has the Food and Drug Administration concerned about neti pot use, is whether people use nice warm water right out of their home tap, tap water that’s boiled or put through a very fine filter, or distilled water.
Not all people get these instructions, though. Maybe they ignore the directions that come with their pot, or maybe they buy one from a ceramic artist who assumes that customers know what they’re doing.
The easiest way to prepare water to squirt up your nose is boiling it and letting it cool. This has the advantage of killing pathogens and heating the water up: let it cool until it’s a comfortable temperature. Commercially available distilled water works, too. A water filter with an absolute pore size of 1 micron or smaller will also catch critters that you don’t want living in your sinuses.
Other nasal irrigation safety tips include washing and drying your hands before you begin, checking the pot to make sure it’s clean, letting it air-dry or drying with a paper towel between uses, and following any additional instructions from the manufacturer.
Unless those instructions say to use tap water. Ignore them in that case.