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Jun 08, 2022 View:

Mash Water Source

If forced to use city water for mashing, do the typical chemicals in processed water kill conversion or fermentation?

Does distillation remove chemicals that impact the taste of the distillate?

Any other comments on mash water impacting distillation would be appreciated!



City supplies include chlorine (from either sodium hypochlorite (like bleach) or more recently and commonly chloramines). It shouldn't be enough to stop a good fermentation, but the chlorine can combine with organic mash compounds to produce some truly awful flavor chemicals in the beer (chlorophenols toward the top of that list).

Some one else will have to address whether these off flavors can make it through the still. I'm curious too.

Free chlorine ions can be removed by heating or aerating, but chloramines are more stable. The typical way to remove these (either) is by adding sodium (or potassium) metabisulphite to the water.

Common practice is to add 3mg of Sodium Metabisulphite per 1mg of chlorine (in theory you only need 1.34 mg of sodium metabite/mg Cl). Municipal supplies are almost all under 2ppm of chlorine as delivered from the tap. So in 100gal of water @ 2ppm of chlorine you have 378.5kg of water => 0.757 g of chlorine and you'll need 3x that or 2.2. grams (less than a teaspoon of powdered) sodium metabisulphite per 100 gallon of that water. [[My water report shows 1.2ppm chlorine for example - do study your local water supply]].

Either type metabisulphite will degrade with exposure to humidity in the air so you should purchase in smaller quantities and keep the remainder sealed and cool.

Until you find a good source of FOOD GRADE sodium metabisulfite you can get camden tables at any wine-making shop. 1 tab is 0.44 grams so you need 5 tabs per 100 gallons in the example above. BTW wine makers use high doses of metabite to stop yeast and alternative fermenters in wine, but that's at 100+ppm in acidic liquids, not 6ppm in a 5.2pH mash.The oxidized sulfites (that neutralized the chlorine) become dissolved sulphates and nearly all tap water has a fair bit of sulfates. By the time you complete the mash I expect all the sulphites will be oxidized to sulphates.


Thanks so very much, stevea, for a truly clear and detailed response! Tremendously helpful. I just got am emil from a distiller in Canada that is using city water. He also refers to using an RO system on their final water... ?


Iron content is another thing that can be an issue. Rarely a problem in tap water but worth testing or asking your source about. It's more likely to be a problem if you are located in an old building or an area with older distribution piping. I worked in a building once where iron content was high enough they would not allow it as potable drinking water and had to bring in bottled water.

My plan is to at least have some level of particulate and chloramine filtration for any water used in mash processing and most likely RO water for cutting spirits to proof. Systems are not super expensive and seem like good insurance against potential off tastes.


Thank you jwymore. Iron is an issue in our ground water. Filtration will certainly be part of my water supply. What is RO?


Duh!!!! I googled it. Reverse Osmosis. Of course!


As a FWIW to a stale thread.

I've found papers that show that hydrogen peroxide can be used to remove the chlorine (&chloramines) in municipal water.

Removing iron is a bit more difficult. I believe the potable limit is 0.5ppm, and it has a flavor effect well below that.

All of the methods involve oxidizing the iron to 'rust' then (optional) filtration. One local municipality simply uses excess chlorine to oxidize iron.

RO Reverse osmosis has the disadvantage of creating waste-water proportional to the amount of clean water needed. I understand that common RO units have around a 50% water efficiency (2 gallon in, 1 gallon of nearly pure water, and another gallon w/ concentrated 'bad stuff') but they can go higher efficiency..


Common RO wastewater ratio is closer to 4:1 than it is to 2:1 (4 gallons wasted for every 1 gallon produced). Poor units setup incorrectly can be even higher yet.

There are strategies to reduce this, but there are typically downsides to all of them, no free lunch.


As some added insight - the off the shelf RO (only) systems can be around 2:1 or 3:1. 4:1 or higher is usually only seen in the off the shelf RO/DI (reverse osmosis/De-ionization) systems. Like everything - quality goes with price (and quality of original water). The commercial systems will pump out RO/DI closer to 2:1 or 3:1 but they are more money.

(FWIW - I was big into salt water reef husbandry years ago so I have done my homework on creating near-pure water to reconstitute into near-ocean saltwater)

If I can extend the topic - what do those of you who do not have access to city water do? I'm guessing my town may be resistant to pulling 1000+ gallons (per week) from the water table from a pump.


I probably ran into you at Absolutely Fish... All my water chemistry and purification knowledge is from reef aquaria. We are actually still using my old Air Water Ice Reefkeeper RO/DI. The small production high rejection filters tend to deal better with lower waste flow, but the high production units really start to jump TDS fast if you slow the waste. These things used to be so expensive that you worried about ruining the membrane with lower flow, but now they are so cheap it doesn't pay to waste the water.


I'd really like to know if folks with relatively decent municipal water are having success with the newer nano filtration systems.


This is old, but you should be able to remove chlorine with a carbon block. RO should only be needed if you are trying to remove iron or the like