UK Homebrewer’s Guide to Water Chemistry and Salt Adjustments

12 November 2026

A quarter of one Campden tablet is enough to treat 25 litres of tap water, and it is the cheapest and most overlooked step in homebrew water treatment. Before you worry about sulphate ratios or mash pH, the water needs to be free of the disinfectant your supplier put in it. Everything else in this guide, from reading a water report to dosing salts and acid, builds on that first step.

Removing chlorine and chloramine before brewing

Most UK homebrewers start from mains water, and mains water is disinfected so that it stays safe on its way to your tap. That is good for drinking, but the disinfectant does not belong in a mash or a fermenter. Chlorine and chloramine can leave unwelcome flavours in finished beer, and they are best dealt with before the water meets any malt or yeast.

The old kitchen remedies only half work. Boiling the water or leaving it to stand overnight removes chlorine, according to the Stonehelm Water Calculator, but neither removes chloramine. If your supplier uses chloramine, which you can find out by asking or by checking your water company's information, a bucket left on the side will do nothing for it. Many brewers skip the question entirely and treat all their water the same way.

The reliable fix is a Campden tablet, made of sodium or potassium metabisulphite. It removes both chlorine and chloramine, and the dose is small: a quarter of a tablet treats 25 litres of tap water. For a typical 23-litre batch you will want to treat the strike water and the sparge water, so work out your total liquor volume first and scale from there. Crush the tablet, dissolve it in a little water, stir it through and let it work before you start heating. A pill cutter and a small jar of crushed tablets make the job quick.

Reading UK tap water reports and profile numbers

Once the water is clean, you need to know what is actually in it. Your local water company publishes figures for the area, and these are the starting point for any adjustment. The numbers to look for are calcium, magnesium, sodium, chloride, sulphate and alkalinity. If your report gives only hardness, you have less to work with, so look for the individual ions or ask the company for a fuller breakdown.

Famous brewing waters give you something to compare against. The Stonehelm calculator lists three well-known profiles, and they show how different the targets can be:

Burton-on-Trent water has calcium at 352 ppm, magnesium at 24 ppm, bicarbonate at 320 ppm, sodium at 54 ppm, chloride at 16 ppm and sulphate at 820 ppm, with a residual alkalinity of -3. Pilsen water is almost empty by comparison: calcium 10 ppm, magnesium 3 ppm, bicarbonate 3 ppm, sodium 3 ppm, chloride 4 ppm, sulphate 4 ppm and residual alkalinity of -6. Dublin sits in between with calcium at 118 ppm, magnesium 4 ppm, bicarbonate 319 ppm, sodium 12 ppm, chloride 19 ppm and sulphate 54 ppm, but its residual alkalinity is 175.

Two things stand out. Burton and Dublin carry almost the same bicarbonate, around 320 ppm, yet their residual alkalinity figures are far apart, because Burton's very high calcium offsets the bicarbonate while Dublin's does not. And Burton's sulphate is more than fifteen times Dublin's. Brewers often describe water through the sulphate-to-chloride balance: sulphate-forward profiles are associated with pale, bitter beers, and chloride-forward profiles with malt-led beers. That ratio is a useful shorthand when you compare your own report with a target.

Your tap water will probably look like none of these. Soft-water areas sit nearer Pilsen, hard-water areas in the south and east may carry plenty of bicarbonate, and the sensible approach is to measure the gap between what you have and what the beer needs. Treat the famous profiles as reference points, not recipes you must copy.

Alkalinity, mash pH, and why it needs adjustment

Of all the numbers on a water report, alkalinity is the one that most often needs attention. It describes the water's resistance to becoming more acidic, and a mash needs to settle in a suitable pH range for the enzymes to work and for the beer to taste clean. If the water is too alkaline for the grist, the mash drifts too high in pH. The usual consequences are a duller, harsher beer and a poorer result from the hops.

Different beers call for different starting points because the grist itself changes the mash. Darker malts bring acidity of their own, so a stout can tolerate, and benefits from, more alkalinity in the water than a pale lager does. The Blue Bottle Brewing guide gives these targets for mash water:

Set these against a soft water such as Pilsen's, with bicarbonate at 3 ppm, and a pale beer needs almost no correction. Set them against water with bicarbonate near 320 ppm and a pale beer needs a great deal of correction, while a black beer needs rather less. This is why a brewer in a hard-water area often finds stouts and porters come out well from the tap while pale ales taste flat or rough.

Alkalinity is the main variable to control because the other minerals mostly shape flavour, while alkalinity shapes the chemistry of the mash itself. Measure the mash pH with a meter or reliable strips, compare it with the style you are brewing, and adjust the water for the next batch. Over a few brews you build up a record of what your water does with each grist.

Burtonisation and choosing brewing salts

Burtonising means adding salts to move your water towards the profile of Burton-on-Trent, whose sulphate figure of 820 ppm and calcium of 352 ppm are the reason the town is associated with pale, bitter beer. You do not need to reach those numbers to see the effect. The principle is that sulphate sharpens and dries the hop bitterness, while chloride gives a rounder, fuller impression of malt.

The Blue Bottle Brewing guide turns that into simple advice. Use gypsum (calcium sulphate) for hoppy beers such as IPAs and pale ales. Use calcium chloride for malty beers such as brown ales and Scotch ales. For balanced beers such as English bitter, use a combination of the two. Both salts supply calcium, so you gain mineral content either way, and the choice mostly decides whether the beer leans towards the sulphate or the chloride end of the balance.

In practice, add salts to the mash water and weigh them on scales that read to a tenth of a gram, because the amounts for a small batch are tiny. Add a little at a time, dissolve fully, and change one thing per brew so you can taste the difference. A common mistake is to add gypsum to water that is already high in sulphate, which pushes bitterness from crisp to harsh. Another is to treat salts as a cure for high alkalinity. Gypsum and calcium chloride bring calcium that helps lower mash pH slightly, but they will not fix very alkaline water.

Using CRS or AMS to reduce bicarbonate in hard water

If your tap water carries a lot of bicarbonate, you have what is usually called temporary hardness, and the alkalinity it brings is the problem for pale beers. Boiling is the traditional way to precipitate some of it, but a measured acid addition is more controllable. CRS or AMS, a commercial acid blend sold for the purpose, reduces the alkalinity of brewing liquor and is widely used for exactly this job.

The arithmetic is straightforward once you have your numbers. The Anglian Craft Brewers brewing water guide works through an example in which removing 130,000 mg of alkalinity from 1,000 litres of water requires 710.4 ml of CRS/AMS. That is 130 mg removed per litre of water. Scale it down to a 25-litre brew length and the dose is 17.76 ml, so the volume is manageable even for a small kitchen set-up.

The method is to subtract your target alkalinity, taken from the table above, from the figure for your tap water, multiply by your volume in litres, and divide the result by the amount of alkalinity one millilitre of your acid removes. The example above implies roughly 183 mg of alkalinity removed per millilitre, but check the strength of the product you actually buy, because the dose depends on it. Measure with a syringe rather than a spoon, add the acid to the water before the grain goes in, and take a pH reading once the mash has settled.

Remember to treat chlorine and chloramine first, since that step is independent of everything above. Then compare your water report with the style you are brewing, adjust alkalinity, and add gypsum or calcium chloride for flavour. Keep notes on each batch, including the mash pH you measured, and the next adjustment becomes a small correction rather than a guess.