Use Prime with your tapwater to neutralize the chloramine. Prime says to use a capful for every 50g of chloramine-treated tapwater. Since I use 3 to 4 gals of tapwater per water change, it would be ridiculous to treat it by the capful. I calculate it takes 3 drops of Prime per gal to treat new saltwater made with tapwater.
I don't think very many people know what's in their tapwater, but religiously use RO/DI or RO only because that's what many reefkeepers advocate. (I used RO/DI for many years and it caused me lots of headaches!) It's a pretty tough sell in modern online reef communities to tell someone to go ahead and use local tapwater because reefkeeping has become so technology-oriented. Technology isn't bad, per se, but it may not always be necessary to do a reasonably good job without it. Using tapwater may be one of those instances for you. You will only know if you try it and either it works sufficiently or it doesn't.
I saw a guy's display and frag tanks a couple of nights ago who used tapwater. The SPS corals in his display, in particular, were stunning! I remember seeing reefs locally before RO/DI became de rigueur and they were quite amazing especially since so little knowledge was available back then.
I don't know what size your tank is, or what you want to put in it. But don't be frightened by nay-sayers that say nay to tapwater. With proper husbandry, your nano will look fabulous
