Just a simple noob water / mash ph question

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Dec 14, 2008
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Ok guys I think I got a handle on the topic of water, I just need some reassurance of my noob ways. My tap water looks like this:

Calculated Parameters
Anion Sum meq/L - 4.9
Cation Sum meq/L - 4.5
Hardness (CaCO3) mg/L - 120
Ion Balance N/A - 0.90
Dissolved Nitrate (NO3) mg/L <0.01
Dissolved Nitrite (NO2) mg/L - <0.01
Total Dissolved Solids mg/L 260
Misc. Inorganics
Conductivity uS/cm - 460
pH 8.23
Alkalinity (PP as CaCO3) mg/L - <0.5
Alkalinity (Total as CaCO3) mg/L - 190
Bicarbonate (HCO3) mg/L - 230
Carbonate (CO3) mg/L - <0.5
Hydroxide (OH) mg/L - <0.5
Dissolved Sulphate (SO4) mg/L 50
Dissolved Chloride (Cl) mg/L 2
Dissolved Nitrate (N) mg/L <0.003
Nitrate plus Nitrite (N) mg/L <0.003
Dissolved Nitrite (N) mg/L <0.003
Dissolved Calcium (Ca) mg/L - 41
Dissolved Iron (Fe) mg/L - <0.06
Dissolved Magnesium (Mg) mg/L - 4.0
Dissolved Manganese (Mn) mg/L - 0.16
Dissolved Potassium (K) mg/L - 0.7
Dissolved Sodium (Na) mg/L - 48

I’ve been using the nomograph in the back of how to brew, it puts my water at 5.93 for mash ph at room temp.( question on this nomograph, do u go vertically from where your line intersects the ra /ph line to determine color or do you follow along your line to where it lands in the beer color?) Furthermore Im assuming mash ph goes down .3ph at 150f mash temp , but it also goes back up after cooling right?

I’m trying to make Bier Muncher’s centennial blonde Ale. My plan is to use 75% RO water to 25% tap water. I plug my tap water numbers in at this ratio and I get a room temp ph of 5.75ish. I believe this might be a little high but I’m using 1.25lb cara-pils ,1lb Carmel crystal and 1lb Vienna malt in addition to the 14lb 2 row base malt. I believe these malts will get me closer to the 4srm rating I'm looking for, but I'm not sure.

One last question, am I risking yeast health or other concerns when diluting my tap water minerals (mg ca ect.) to such low quantities as ca to 10 and mg to 1?

Thanks in advance for you help
happy st patricks day