More bitternes with tap water?

I don't know how to understand, evaluate and adjust my city water for brewing but I starting to come to conclusion that my city water is a little hard. If I use 100% tap water my brews become really bitter even with just 20-30 IBUs if I mix it with 80% RO water I usually get good results, smooth beers and hops take a back seat. Its good for some styles and not so for others. Can you please lead me in right direction, how is my water and what should I do? What proportions I should mix it with RO? Would 5.2 ph stabilizer be a good idea in my mash? Thanks.

Water Quality Parameters

Did you read the primer in the stickies section of the Science threads? Personally I like to brew with RO water only and adjust with some Cal Chloride and Gypsum. You could do the dilute thing as you found out.

The usual suspect in a case like yours is sulfate but your city report doesn't list it. It also doesn't list alkalinity, the parameter the brewer looks at first. Call the city and ask about alkalinity and sulfate and if they don't give you an answer, or even if they do, send a sample off to Ward Labs for analysis.

I just got a call back from city and they say that Alkalinity is 185 mg/L (ppm), Sulfate is 58 mg/L

These data fit your observations. Now what to do for the various styles of beer is a broad subject. Dilution with RO at the 80% level effectively defeats the sulfate and the alkalinity. If you want more hop punch, you can replace the sulfate. If you are doing a dark beer with lots of acidic malt you will need to replace the alkalinity (or not dilute so much unless you want to suppress sulfate).

The Primer is a good place to get started.

Thanks! I'll order some brewing salts and learn to use them