Could someone put me right on this?

[butterman]

If their tap water is high in mineral content, then adding RO water will dilute it to more desirable levels.

Is there an objective method (or if not, a rule of thumb) to tell you how much to add to get to a certain mineral level (desired level). From my OP it seems using a pH meter wouldn't help!

Pretty simple actually. Let's say your water report says you have 100ppm of calcium. Mix 1 gallon of your water with 1 gallon of RO, you now have 50ppm. Just remember to do the same math to each mineral.

Now, that really makes common sense to a non-chemist type like me, who previously wasn't able to see the forest for the trees. Thanks for your input.

[spiderwrangler]

Now, that really makes common sense to a non-chemist type like me,

We should have had madchemist explain it to you... because as everyone knows, he's a chemist...

[Ozwald]

No worries. Most of the water chem revolving around brewing is far easier to understand than what it seems like. Kind of like getting into all grain, it's mysterious & daunting until you do it & realize how simple it really is. Also note you don't have to do a simple 50-50. You can dilute it with whatever percentage - 25% of your 100ppm water to 75% R.O., you now have 25ppm (1/4 of the water is tap, so take 1/4 of the mineral content). You can make it as easy or as complicated as your personal math skills allow.

For practical usage, it's a really useful technique if your water has way too much of a particular mineral. For example, Palmer states that 50-150ppm of calcium is considered the range for brewing. If you have 300ppm coming out of the faucet, you'll have to cut it to get down into the ideal range. You just have to remember to cut the rest of the minerals by the same amount. If another mineral is in the ideal range before you cut it, you'll have to build the water back for that particular mineral.

[BrewChemistinCO]

Pretty simple actually. Let's say your water report says you have 100ppm of calcium. Mix 1 gallon of your water with 1 gallon of RO, you now have 50ppm. Just remember to do the same math to each mineral.

Now, that really makes common sense to a non-chemist type like me, who previously wasn't able to see the forest for the trees. Thanks for your input.

Just to add one more small statement, pH is kinda the summary of everything in the water. There are too many different ions to be able to take a pH reading and say that you have 133 ppm calcium.

As Ozwald says, your water report is the only practical way of finding out what your starting point is.

From there, most brewing water chemistry is as simple as Ozwald says in his follow up post.

[spiderwrangler]

Just to add one more small statement, pH is kinda the summary of everything in the water. There are too many different ions to be able to take a pH reading and say that you have 133 ppm calcium. .

Yeah, thats what I was trying to say