I steal a bottle of the distilled water hubby buys to top off the batteries. (Shhhhhh!) But not because of possible funky bacteria- we have really hard water. I see what the mineral deposits do to the shower head and the boiling kettle just in one week. I can only imagine what it'd do to my sinuses! That would be counter-productive, no?
My partner recently turned me on to using the Neti Pot and at first I didn't believe him that it works. However, after trying it out a few times I must say that I was wrong. It's pretty awesome. I do it about once a week to keep my sinus clean. I read through the brochures that came with my Neti and they will tell you not to use plan tap water. You are sending water up to a sensitive area of the body so why would you want to damage your sinuses.
I have been using a neti pot at least once a month for years with tap water, both here in the desert and in Hawai'i and have not had any problems. I use the saline solution packets and mix with warm tap water. As a matter of fact, I used it yesterday. J has been fighting off a cold and I woke up a little stuffed up and puny feeling. After taking a shower, I used the neti pot and spent a couple hours sitting in the sun. Today I woke up feeling great and ready to go!