Tapwater's not as scary as some say it is. I found it a nuissance, myself, compared to RO/DI water, but not a danger.
When I was running tapwater, I had a massive hair algae bloom from cycling my rocks, but there were too many factors to really account it as being the tapwater. For one thing I made the mistake of running a photoperiod while the rocks were cycling. My diatom bloom lasted about a week longer than it did in my 18g nano, but it cleared out a week before the hair algae attack.
Also, my algae went away when I both switched to RO/DI water, and added the phosphate reactor, AND added the skimmer in the same 2 week period, so I can't determine whether one helped more than the other. I don't want to stop using any of them, as well, out of fear of an impending bloom
One thing I did notice is that with RO/DI water I'm not using prime any more and it made my skimmer more managable. I switched to RO/DI water, then I ran carbon to rid it of the remaining prime (as euroreef instructed me to do) and the skimmer quietted in about 3 days.
Not that I'm knocking tapwater, I just feel safer using it on my big tank. I've used tapwater for quarantining fish, and I'm probably going to use it for cycling liverock from now on, too.