When you're using extracts, distilled is not only okay, it's preferred. Makers of extract, whether dried or "wet," use a balanced mineral profile that is ideal for brewing. Thus, when the extract is reconstituted, the mineral profile is preserved. Dried extract is generally better for distilled or RO/DI water, but both forms are acceptable. I did quite a bit of math to arrive at this conclusion, so I'm not going to repeat it all here, but trust me on this one.
However, if you're going all-grain, minerals will need to be added. Somewhere between 3-5 tsp of Burton salts will do the trick. Ideally, you'd be using a TDS meter along with profiles of notable brew waters. If you really want to drive in with both feet, you'd need the powdered forms of all chemicals present in given brew waters, adding minute amounts of each until that profile is exactly duplicated. Some brew places actually sell the powder mixed precisely, one for Burton, one for Dublin, one for Edinburgh, etc.
I like distilled or RO/DI water for brewing because of the control it affords. A lot of folks use tap with the "eh, whatever" mentality, and I'm not saying that's wrong, but it's not for me.