Distilled water Water treatment is not 100% effective at removing protozoa and amoeba. Though in general it is if everyone is doing their job's right. In the stomach, acid and digestion tends to take care of them pretty quickly. If they survive to enter your blood stream through an ulcer your immune system is generally on top of them because of the length of circulation. Even if they don't get into your blood stream and they multiply, they generally pass with diarrhea (though some complications are still possible in liver or kidneys). And that's that. This infection pathway has many layers which generally keep you safe and healthy. Even if they infect your organs, treatment is generally available. This all changes if the vector is your sinus. The sinus is very close to your brain. It doesn't require a long trip across this barrier to get into your brain. The sinus delivered potential pathogens directly adjacent to your brain. Which completely avoids processing by your stomach and other organs. The result is usually a terrible outcome. Distilled water is filtered and boiled. It's safe for use in your sinus.