If your tap water tastes good, your beer will taste good. Just try it. You will not notice a difference. And you will save time and money. If you are worrying about water, you are probably worrying about the wrong thing. On brew day, the first thing I do is fill my brewing vessel with 6 gallons of hot water directly from the kitchen tap. Yes, hot water. Then, I brew the beer and it tastes good.
I admit, for my first few batches I used filtered water, because I took a tour of Bell’s Brewery and the lady said that Bell’s essentially uses a giant Brita filter. So I did. That’s fine, but I’m not making commercial beer. And it was a huge pain in the ass. I had one of these half gallon Brita filters that goes in your fridge. Fill it up, wait for it to filter, pour; fill up, wait to filter, pour. It took like 15 minutes just to begin brewing, spilling water all over the fucking floor like a clown.
If you are making a historical beer (like a British Porter from the 1700’s or something) – sure, go for it. Or, if your water sucks, then go buy it. All I’m saying is this: first try tap water and see how it tastes. Second: don’t try to act like commercial breweries all the time.