In Mitch Steele’s book on IPA’s, the following is mentioned in the Stone IPA recipe:
“Municipal water (300 ppm hardness) is carbon filtered and goes through a reverse osmosis process. Treat to reduce hardness to 100 ppm”. How would that work? Boil the water? Add acid? But how does this go together with reverse osmosis?
From the tour at Stone, they have a big RO system to remove the high mineral content in the water. Then they blend the tap water with RO water to get the hardness they want. Simple as that.
Edit - there were also bags of CaCl2 and Gypsum stacked high. If those were added to the mash water or the boil kettle, I don’t know. Sierra Nevada does add kettle salts, I have seen that in person.
There is also something called “nano filtration” which is selective type of filter. That said, I wouldn’t worry too much about Stone’s process, what matters is YOUR water. If you have 300ppm hardness then you will likely need to do something similar to Stone and dilute. However if your water is 150ppm or less then no need to dilute and you can treat with just acid.
They might use multiple techniques. RO will certainly remove the bulk of the hardness. Heatup after would rock up even more of it if desired. Chemical additions might also be used (possibly phosphoric??).
I agree with Sandusky Sam on the bottom line – the particulars are not as important as the end result.
So Ca + Mg would be 100 ppm. That’s a bit lower than Martin’s pale ale profile with Ca+Mg = 160. Right? I’ll reduce the other minerals the same way.
Still, from http://srcity.org/departments/utilities/h2o/h2oquality/Pages/default.aspx
“Santa Rosa Water is considered to be moderately hard at an average level detected of 93.6 ppm or 5.5 grains per gallon.”
So that’s quite a discrepancy. But ok, doesn’t really matter to me then.
(where the heck is Martin when you need him ;D) I think you are confusing some things (hardness vs ca/mg although they are related) How’s about a screen shot of BNW water profile screen? I think your water’s probably fine…
Yeah, I’m confused by the 'Ca + Mg" thing. Regardless of water profile, Mg content IIRC is sub 17ppm in Brunwater. Pretty nominal.
You can reduce to about 60-80 ppm using lime treatment.
The descrepancy is that Stone is in Escondido CA, 550 miles from Santa Rosa CA! 
High TDS and the average hardness is 255, high 300, as ppm CaCO3.
http://www.escondido.org/Data/Sites/1/media/pdfs/ccr2015eng.pdf
California has a very mixed geology, parts will have soft water from granite aquifers, other parts have sedimentary layers and hard water. Southern CA also uses water from the Colorado River, which is full of minerals. From a quick internet search.
Hardness depends on the Ca and Mg content. You can look it up in Brunwater or the web.
Ouch, confused with Russian River location 
Frank, no problem, as you are a long way from CA.
It IS a problem. I’ve been to Santa Rosa. I need to call my therapist.
I think you mean bartender.
I took the original quote as meaning RO is what reduces hardness. I haven’t had the behind the scenes tour but I wouldn’t be surprised if they also used some acid.
Also hardness (expressed as ppm CaCO3) is not exactly the same as ppm of the ions.
Hardness = (Ca ppm) * 2.5 + (Mg ppm) *4
Damn, two variables in an equation, an infinite number of solutions. 
Your formula is for permanent hardness. Would be around 32 ppm Ca and 5 ppm Mg. But do we know that the 100 ppm is permanent hardness?
Just asking for fun now. If I brew this I’ll just use an APA or IPA profile with demi water.
Total hardness is what is I posted above, and is the concentration of Ca and Mg. Alkalinity is carbonates. Temporary hardness is the portion of Ca and Mg that is balanced by carbonates and can be removed by boiling. Permanent hardness is the rest, what cannot be removed by boiling.
Total hardness is what Mitch is talking about, I assume.
Also, if you experience permanent hardness (or more than 4 hours of it) you should see a doctor.
How do you measure ppm?