Q:

How do I test my water?

Inspired by this question. How do I test my water?

A:

If you have city water, they usually sent out a water profile a couple of times a year. It will be an average of the whole city, but it'll give you a general idea of what you're dealing with.
You can also send your water away to a lab to get tested. I've never bothered, so you'll need to find a reputable lab.

A:

A city water report is the first place to look, but given where your city gets it's water, the values can fluctuate pretty significantly. For example, my city gets water from a few sources; sometimes they'll mix in well water, and thus the water has higher hardness, or they might be taking surface water shortly after a fresh rain.
The question to also ask is "why" should you test your water. To answer that, a good starting point are sections 15.0 though 15.4 in Palmer's How to Brew:
http://www.howtobrew.com/section3/chapter15-1.html
Water chemistry does have a significant affect on beer flavor. Often water chemistry is the last bit of tweaking needed to make a good beer great.  Having said that, it's also an easy way to muck up a beer. Water chemistry (aside from proper filtration) should be your last concern in making beer.  Sanitation, yeast handling, temperature control, recipe formulation and brewing process should all come first.

