Water Quality Question

Pretty new to all of this, but have a quick question about water chemistry. I'm on city water supply and i've got an email in to my water company asking about a water analysis. But i've done some tests using a water test kit i've got for my hot tub which allows me to measure total alkalinity (100-110 ppm), pH (7.4) and calcium hardness (90 ppm). I've got an under the sink water filter also. It seems like a lot of people out there are going out an buying RO or DI water for their brews. I know that beer is mostly water, so that can have a pretty darn important affect on the outcome of your beer, but what is it I should be worried about with my tap water? My filter takes out any of the chlorine smell of tap water, and it seems to drop the pH to about 7.2, but otherwise the total alkalinity and calcium hardness don't change. I'm sure i'd want to use the water from the undersink filter and not straight tap, but do I need to start with store bought water? or is that for people who have something really wrong with their water? I've got plans to make an oatmeal stout (extract kit) as well as my first all grain beer, a sMasH of marris otter and kent goldings.

Any help is appreciated.

Sounds like you're using an activated charcoal filter. That will be good for taking out chlorine, but if you want to remove minerals, you need an RO system or at least an ion-exchange filter.

Also, it's worth mentioning that the pH of the water isn't that important- the mineral content and grain bill will determine your mash pH which is the important pH to take.

I wouldn't worry about the extract kit as much and just use your filtered water because that wort was already made with water appropriate for that style and then just dried so adding your filtered water shouldn't hurt. I've been doing a bit of studying on water profiles and what it does to the PH during the mash and here are a few guidelines that I've found from AJ DeLang that really help when setting up a water profile:

https://www.homebrewtalk.com/f128/brewing-water-chemistry-primer-198460/

Hope this helps.