Water report v Home testing

[MillmoorRon]

My local water report does not give a value for alkalinity however they did supply me with the test results over the previous year. These ranged from 7.7 mg/l CaCO3 to 480.43 mg/l CaCO3 with an average from 42 samples of 119.84. Due to this massive potential range, I guessed it would be better to test the water myself immediately prior to a brew.

I acquired a carbonate hardness kit and over several tests across the last few months it has been consistently around 130 mg/l CaCO3.

I also now have a general hardness kit and this is reading approximately 16 degrees of German Hardness. (285.6 mg/l CaCO3) which is right at the top end of the water report's range for the last 2 years.

From my water reports, the magnesium content averages about 6 but has not exceeded 8.2 mg/l.

Using the formula: Hardness = 2.5 x Ca + 4.1 x Mg and taking the maximum Mg content, I estimate my Ca content to be 100.8 mg/l, which is at the top of the range given in my water reports.

Then using the formula: Residual Alkalinity = Carbonate Alkalinity - (0.71 x Ca + 0.59 x Mg) I get a RA of 53.6

Is my reasoning correct?

[BenB]

I'm sure those with superior knowledge will be along but here's my thoughts...

That's a very significant swing. Certainly home testing is going to be important with that variability. RA is not accepted by all as terribly useful especially with dark beers. Equally, it seems to work for me as I understand Bru'N water relies on it for pH calculations and they seem to work nicely for me...

Can't see any fault in your reasoning though. I'd be tempted to get a Calcium test kit (seems simpler to measure that than work out total hardness and then guess the magnesium level, do some maths etc etc).

Magnesium isn't going to be that important as the levels appear low.

Alkalinity is the most important bit. Calcium as long as you've >50 (preferably >100) it's all good. More doesn't hurt. Magnesium doesn't matter too much unless you've got laxative levels (tons of the stuff).

So I'd test alk and Ca prior to a brew, assume Mg at 6 and go from there in terms of building up a water profile.

[alexlark]

You can get pretty good home water analysis using the Salifert Hardness and Salifert Calcium test kits.

[MillmoorRon]

I tested with a Salifert Calcium kit but the levels were quite a bit lower than expected from my earlier tests. I then retested the General Hardness and Carbonate Hardness and they have changed dramatically in 9 days!

My previous results (all in mg/l CaCO3) were 286 (GH) & 117 (KH) but the latest test was 142 (GH) & 57 (KH), which do at least tally with the Calcium results.

Is it normal for these things to change so much in such a short time?

[rpt]

I'd say yes. Depending on where you live, the water company can change source quite easily. My alkalinity varies between 5 and 70ppm as CaCO3.

[Aleman]

Certainly can, my alkalinity can go from 16.8 up to 135, with a subsequent rise in calcium as well.

[Eric]

95mg/l calcium and 250mg/l alkalinity as calcium carbonate this morning. For my two brewdays last month alkalinity was 93mg/l and 178mg/l. Provided you can measure it, you can deal with it. Get it tested when the readings are high and when they are low and you might find each component has for all practical purposed a fixed relationship with all others.

[alexlark]

I've been testing mine before each brew for the last 7 months. Building up a picture of the water over the course of a year.