Water for the beginning all-grain brewer

I'm preparing to brew my second batch of beer from extract. I brew outside with a 8 gallon pot and would like to make a MLT and try all-grain for my 3rd batch. But my city's water report is incomplete at best (I do know that Sodium is 140, Sulfate is 101 and Mg is non-detectable). Is it necessary to have a complete water analysis in the beginning? I'm thinking of starting with a Robust Porter and would like to do a Belgian Strong Dark Ale.

If you don't want to get your water tested at a place like wardlab.com, your next best choice is to buy RO or distilled water and build it from there. I can tell you right now that your sodium is too high and Mg is too low. It sounds more like the output of a water softener than anything else.