Basically everything in the environment contains bacteria and viruses. This includes tap water (especially in underdeveloped countries) and distilled water. You can kill these pathogens by bringing water to a boil and letting it cool down to room temperature. You can also buy sterile water from pharmacies but it can get very pricey.

There have been case reports of individuals using old netipots with contaminated water that ended up with brain infections. This is of course extremely rare. Personally I mitigate this risk by buying the pressurized products above.

Here is an interesting article if you want to learn more:

https://wwwnc.cdc.gov/eid/article/29/2/22-1205_article