Yeah... knowing tap water can- make that DOES- harbor pa and other bugs, shooting that up into her sinuses makes no sense whatsoever after all we go into to sterilize nebs, do cpt and keep their environment clean! I have assumed that once a container has been opened it's not sterile anymore so I only make what I need for one use. When Emily is congested, she generally needs about 24oz of water to thoroughly flush her sinuses (we do it until the water flows mostly clear; the first bottle barely starts loosening things up.) Boiling it in a Pyrex in the microwave and then letting it cool down (cover the top) prior to use also works well.