for the most part, i don't use tap water. Bought a sweet r/o setup for 130 bucks, my tapwater is outrageous due to all of the agriculture. Tapwater can be ok and at the same time a lot of people don't like it. If your tapwater has 400ppm in it, then that's 400ppm of of balanced nutrients you can't add to the solution... 0ppm filtered water gives you complete control over what nutrients your plant gets, that's good for some people and bad for others. For outdoor growing and soil, i will use ph adjusted tapwater, but i also do mostly orgranic with only one or two additives... For hydro, i only use r/o or distilled water.
Here's the r/o i bought. Been using it for 6 months on the same filters, no leaks. Has a backwash, built in pressure gauge, automatic system shut off valve, and uses a ge membrane which is one of the better brands.
http://www.marinedepot.com/ps_viewi..._campaign=mdcsegooglebase2&utm_content=vx3131