Rainwater or tap? Our tap water here has fluoride and other treatments are done to it. I use my own collected rainwater but that is not even very good in some places (not a problem here)
I never spray my indoor plants once buds are starting to develop (unless flushing after spraying bugs)...probably why the spider mites like them so much.
Bugs in buds do not necessarily mean no chems...I use all sorts of shit to kill the little fuckers when they find their way in.