Tap vs. distilled for calibration

[FenoMeno]

When calibrating my Refractometer and taking note of my Hydrometer, how important is it to use distilled water?

I noticed via brew software that temps within 5* give the same results, so I was wondering if tap would be in a close enough window for this.

 

[auburntsts]

My guess is it would depend on your tap water's chemistry which is most likely never constant. Assuming the same water temp, distilled water and tap water will have different densities due to the stuff dissolved in the tap water which won't be present in the distilled water. The question is what's the magnitude of the difference and its impact on the calibration of the refractometer.

Seems to the easiest solution is to calibrate with distilled and not try to figure out any kind of correction factor.

 

[ancientmariner52]

The correct answer is, of course, distilled water. The practical answer, as Auburntsts states, is 'depends'. My tap water is very low in dissolved solids. I rationalize my bad habit by reasoning that I don't need to know absolute sg, I need to know what has changed, in the mash and fermenter. So I check calibration of my refractometer with my strike water, so I know any change is caused by sugar extraction.

By the same reasoning, I take an og hydrometer sample from the fermenter for comparison with fg samples with the same hydrometer. It's important to use the same hydrometer because what matters is the amount of change, not the absolute numbers.

Or get some distilled water, and ignore the above. Probably the best plan.

 

[jalc6927]

I tried both ways, you need distilled water at 60 degrees

Just grab a 12 oz bottle

 

[Ozarks Mountain Brewery]

make sure you use the correct amount of water your packet states. the last time I was in a hurry and just used too 2 whiskey glasses and filled them 3/4 full and didn't measure and never could calibrate perfectly, I just split the difference, but you can buy a gallon of distilled water at the grocery store for a buck here I use it for yeast also

 

[FenoMeno]

The correct answer is, of course, distilled water. The practical answer, as Auburntsts states, is 'depends'. My tap water is very low in dissolved solids. I rationalize my bad habit by reasoning that I don't need to know absolute sg, I need to know what has changed, in the mash and fermenter. So I check calibration of my refractometer with my strike water, so I know any change is caused by sugar extraction.

By the same reasoning, I take an og hydrometer sample from the fermenter for comparison with fg samples with the same hydrometer. It's important to use the same hydrometer because what matters is the amount of change, not the absolute numbers.

Or get some distilled water, and ignore the above. Probably the best plan.

Thanks, I agree with your above technique and use the same technique for the most part. Agreed that the change is what I'm looking for. Using Hydro/Refract for OG, Refract for "changes" during fermentation, and a larger scale 2nd Hydro for the FG.

I was curious of the magnitude of the difference for tap water. I understand this will be different per location tap, but if that difference is insignificant, I'll save myself a trip to the store for distilled. --btw, I'm setting up my brewing software for Mash/BH efficiency as using this info to dial those in.