Digging Deep into Water Treatment

[strange-steve]

What is alkalinity?
Essentially, alkalinity is a measurement of a solution's pH buffering capacity, its ability to resist change in pH. The higher the alkalinity, the more resistant the water is to a change in pH because the ions responsible for alkalinity neutralise acids by absorbing H⁺ ions. In other words, more acid would be required to lower the pH of high alkalinity water compared to low alkalinity. This seems to be a common source of confusion, because alkalinity often gets conflated or confused with pH, hardness, or basicity, which are related but not the same thing.

Now the water coming from our taps contains various dissolved minerals and ions, some of which contribute to alkalinity. The three main sources of alkalinity are carbonate, bicarbonate, and hydroxide [1]. The carbonate (CO₃⁻²) and bicarbonate (HCO₃⁻) ions typically find their way into water from CO₂ absorption (forming carbonic acid initially) and from geological sources when precipitation runs over or through soil and rock. The hydroxide ions (OH⁻) on the other hand are a natural part of water due to the self-ionisation reaction mentioned earlier.

The alkalinity equation
So the total alkalinity is a sum of these negatively charged ions minus the positively charged hydrogen ions:

Alkalinity = (carbonate x 2) + bicarbonate + hydroxide - hydrogen ion

(Note: carbonate is multiplied by 2 because it has a -2 charge meaning it can react with 2 H⁺ ions)

To help get a more intuitive understanding of this and how it applies, let's look at some simplified examples. Pure water, with no carbonate or bicarbonate, and equal amounts of hydrogen and hydroxide ions (ie pH neutral) will have an alkalinity of 0:

Alkalinity = (0 x 2) + 0 + 1 - 1 = 0

This also helps us see the relationship between alkalinity and pH. Typically as the pH gets lower (ie H⁺ increases) the alkalinity will reduce and as pH increases, so does alkalinity. Look at the following two sums, the first one is a basic solution (more hydroxide than H⁺) and the second one is acidic:

Alk = (4 x 2) + 4 + 8 - 6 = 14
Alk = (4 x 2) + 4 + 6 - 8 = 10

Notice that when the carbonate and bicarbonate remain the same, but the pH is reduced it results in lower alkalinity. Now these aren't real world examples, these numbers don't mean anything, but hopefully they help you to get a more intuitive understanding of how alkalinity and pH are linked but are not the same.

 

[strange-steve]

Alkalinity as a buffer
These simplified examples should also help with understanding the definition of alkalinity, ie that it's a measurement of the pH buffering capacity of a solution, because the higher the alkalinity is the more stuff there is to react with H⁺ ions. If an acid is added (ie increased H⁺) these react with the carbonate or bicarbonate like so:

CO₃⁻² + H⁺ = HCO₃⁻
HCO₃⁻ + H⁺ = H₂CO₃ ⇔ H₂O + CO₂

The H⁺ ions from an acid addition are "absorbed" by the ions responsible for alkalinity and so the H⁺ concentration doesn't increase (or increases only a little) meaning that there is no appreciable change in pH. If there are no carbonate/bicarbonate ions (ie zero alkalinity) however then an acid addition will immediately lower the pH. This is how alkalinity resists changes in pH and this is why it's important for brewers, but more on that later.

The effect of pH on alkalinity
You may have read that for brewing the pH of the water has little impact on the mash pH, and that alkalinity is much more important. This is true, and to show why let's plug some realistic numbers into the above formula [4]. Say your tap water has a pH of 8, has 0 carbonate, and 120ppm bicarbonate; after converting to mEq/L we have this (don't worry about the actual calculation yet, this is just to help to understand the small effect of pH):

Alk = (0 x 2) + 1.97 + 0.001 - 0.00001 = 1.97099 mEq/L = 98.55 ppm as CaCO₃

This is what would happen if the pH was 6 instead:

Alk = (0 x 2) + 1.97 + 0.00001 - 0.001 = 1.96901 mEq/L = 98.45 ppm as CaCO₃

If you didn't follow these calculations don't worry, the point is that the pH makes very little difference to the total alkalinity, only 0.1 ppm in this example with a 2 pH drop. This is because at typical tap water pH levels OH⁻ and H⁺ ions exist in very small numbers compared to bicarbonate. For this reason the starting pH of your water isn't really relevant as far as we're concerned and so the alkalinity equation can be simplified to this (which is often called carbonate alkalinity for obvious reasons):

Alk = (carbonate x 2) + bicarbonate

A note on carbonate
You may have noticed that in the above examples the carbonate was 0. The reason for this is that carbonate doesn't really exist naturally in water below about pH 8.3, at least not in any significant amount [8]. Below this pH the increased concentration of H⁺ ions react with carbonate to form bicarbonate like so:

H⁺ + CO₃⁻² = HCO₃⁻

Therefore if your tap water has a pH of <8.3, which it typically will, you can ignore carbonate because it has all been converted into bicarbonate. That means that we can once again simplify our alkalinity equation above to get this:

Alkalinity = Bicarbonate

Now this may seem too easy, and of course it is. To properly use this equation we need to use the correct units, and this is where things get complicated.

 

[strange-steve]

Units of alkalinity
The equation we've been using up to now is a stoichiometric formula and so is based on molecules or moles, but we can also use the units mEq/L, and to avoid confusion this is how the simplified alkalinity equation should be written:

Alkalinity (mEq/L) = Bicarbonate (mEq/L)

But there are several different ways that alkalinity can be, and is, reported which does in fact cause a lot of confusion. Let's look at some of these to see how or why they're used and how to convert them to something useful. So let's stick to mEq/L for now.

mEq/L
This stands for milliequivalents per litre which is equal to millimoles per litre times the charge of the ion. For example, bicarbonate has a charge of -1, so 1 mmol of bicarbonate (61 mg) in 1L of pure water equals 1 mEq/L (ignore the fact that it's a negative charge it's the quantity that's important).

Carbonate has a charge of -2, so 1 mmol of carbonate (60 mg) in 1L of pure water equals 2 mEq/L.

This may not be the most intuitive way of thinking about alkalinity, at least initially but once you've gotten your head around it it's probably the clearest and easiest unit, particularly with regards to our alkalinity equation above. If you know the bicarbonate concentration in mEq/L then you know the alkalinity in mEq/L, it's the same. We can also work backwards from this to work out bicarbonate concentration in mg/L or ppm* by multiplying by the molar mass of bicarbonate which is 61g:

Bicarbonate (ppm) = Alk (mEq/L) x 61

*Note that ppm (parts per million) and mg/L can be used interchangeably here because 1mg equals 1 millionth of the mass of 1L of water (1kg). Technically this is only true for solutions with a specific gravity of 1 at 4°C, but the difference for our purposes is practically zero.

ppm as CaCO₃
The most commonly used unit for alkalinity, at least in the homebrew world, seems to be ppm as CaCO₃ (calcium carbonate) which is a common source of confusion. Partly because this is the same unit of measurement often used for hardness, but also because calcium has nothing to do with alkalinity, and (at typical tap water pH) there's likely little to no carbonate in the water, so what gives? Well I really don't know why this unit is used, but it represents alkalinity in terms of the amount of calcium carbonate that would theoretically need to be dissolved in water to give the same alkalinity [5].

For example, an alkalinity of 100ppm as CaCO₃ is equivalent to 100mg of calcium carbonate dissolved in 1L of water, but how does this correspond to mEq/L? Well CaCO₃ has a molar mass of 100g, so 100mg in 1L equals 1 millimol per liter of CaCO₃ equivalent, and as mentioned above carbonate has 2 mEq per millimole. Therefore 100ppm as CaCO₃ equals 2 mEq/L, meaning the conversion is as follows:

Alk (ppm as CaCO₃) = Alk (mEq/L) x 50

From this and the previous equation we can substitute and rearrange to find the conversion from alkalinity as CaCO₃ to bicarbonate:

Alk (ppm as CaCO₃) = (bicarbonate (ppm) / 61) x 50 = bicarbonate (ppm) / 1.22

dKH
Another unit of alkalinity measurement often used is dKH, a German unit of measurement which stands for degrees of carbonate (karbonathärte) hardness [6]. This is another potentially confusing term because it again conflates hardness with alkalinity, especially because the term carbonate hardness is also sometimes used to mean temporary hardness. For that reason it's probably best to ignore this unit of measurement, but be aware that 1 dKH is equal to 17.86 ppm of CaCO₃. In other words the conversion is:

Alk (ppm as CaCO₃) = dKH x 17.86
Or
Alk (mEq/L) = dKH x 0.36

CO₂ equivalence point
At this point it should be noted that there is another way of determining alkalinity without knowing the ionic content of the water, ie an experimental method, which is through acid-base titration [7]. This method measures the amount of acid required to reduce a sample of the water to a specific pH, usually 4.3. From this the alkalinity can be determined, and in fact this is how alkalinity test kits such as the Salifert KH kit work. This pH is known as the CO₂ equivalence point, and is the point at which all bicarbonate is converted to carbonic acid by the increased H⁺ concentration like so:

HCO₃⁻ + H⁺ = H₂CO₃

This is the point at which alkalinity reaches 0, because there is no carbonate or bicarbonate left. The actual endpoint isn't necessarily pH 4.3, it can vary from this and is often cited as 4.5, however in most cases this is a reasonable assumption.

Another interesting and related point to be aware of should be apparent from looking at the original alkalinity equation mentioned above: Alkalinity = (carbonate x 2) + bicarbonate + hydroxide - hydrogen ion. Because of the negative element in the equation, the hydrogen ion, it is entirely possible to have a negative alkalinity value. If the H+ is greater than the sum of the carbonate species (CO₃⁻², HCO₃⁻, and OH⁻) then the alkalinity value will be negative. This will only occur in water with a pH of less than about 4.3, when all carbonates have been converted into carbonic acid. For our purposes, we shouldn't be using water this acidic and so this point won't be of practical relevance, but you should be aware of it at least.

Hopefully now we have an understanding of pH, alkalinity, and what causes it, so in the next part we will look at why this is important to brewers.

 

[strange-steve]

References
[1] https://www.sciencedirect.com/topics/engineering/alkalinity
[2] http://www.iupac.org/publications/pac/1985/pdf/5703x0531.pdf
[3] https://sciencing.com/alkaline-vs-basic-6132782.html
[4] https://sciencing.com/calculate-alkalinity-5135624.html
[5] https://www.advancedaquarist.com/2002/2/chemistry
[6] https://en.m.wikipedia.org/wiki/DKH
[7] https://www.water-research.net/index.php/the-role-of-alkalinity-citizen-monitoring
[8] https://or.water.usgs.gov/alk/faq.html

 

[bobukbrewer]

Some 5 years ago I did my own research and concluded that half a campden tablet was plenty for 34 litres of my tap water (30 minutes) - before adding 20 ml of AMS (left overnight) was ok for my pale 3.8 % bitters. I use safale 04 yeast one sachet to 200 ml bottled water to which I add 8 gm brewing sugar and a tip of vitamin C and a tip of nutrient. My vitamin C is genuine vitamin C purchased from a specialist supplier because I take 5 grams a day on the odd occasion I get a cold. I have never had off flavours in my beers...yet

 

[Argentum]

Part 2 - Alkalinity Adjustment

2a - Understanding alkalinity

... snip ...

H⁺ = 10-2.5 = 0.0032 mol = 3.2 mg/L

An excellent presentation, but the molar relationship as you have expressed it (valid only for the case of strong acids with complete dissociation) is confusing, and may better be expressed as:

H⁺ = 10^-2.5 = 0.0032 mol = 3.2 mg/L

10 is being raised to the power of -2.5, so as to express pH as a molar concentration. The '^' or caret sign indicates "raising to the power of".

 

[Rodcx500z]

Wow and wow how do you take all this in then write about it, way over my head but thanks for taking the time and effort, I have never taken the time to think about water but the other day I was filling the dogs bowl up and got a good whiff of chlorine so I checked water report this is what I get

• Summary
• Full

Analysis Typical value UK/EU limit Units
Hardness Level Soft
Hardness Clarke 1.47 Clarke
Aluminium 31.3 200 µg Al/l
Calcium 7.41 mg Ca/l
Residual chlorine - Total 0.60 mg/l
Residual chlorine - Free 0.53 mg/l
Coliform bacteria 0 0 number/100ml
Colour <0.793 20 mg/l Pt/Co scale
Conductivity 57.4 2500 uS/cm at 20oC
Copper <0.0022 2 mg Cu/l
E.coli 0 0 number/100ml
Iron <5.99 200 µg Fe/l
Lead <0.343 10 µg Pb/l
Magnesium 0.646 mg Mg/l
Manganese 1.11 50 µg Mn/l
Nitrate <1.18 50 mg NO3/l
Sodium 3.20 200 mg Na/l
This means nothing to me except Steves efforts on this made me look so thanks Steve I appreciate this a lot, what I am asking now is do I need to use campden tablets also notice we have soft water do I need to make it harder, thanks again

 

[strange-steve]

An excellent presentation, but the molar relationship as you have expressed it (valid only for the case of strong acids with complete dissociation) is confusing, and may better be expressed as:

H⁺ = 10^-2.5 = 0.0032 mol = 3.2 mg/L

10 is being raised to the power of -2.5, so as to express pH as a molar concentration. The '^' or caret sign indicates "raising to the power of".

You're absolutely correct, that's what I had intended to write. Though I'll be surprised if a missed caret (I didn't know that's what it was called either) is the only error here :thumba:

 

[strange-steve]

Wow and wow how do you take all this in then write about it, way over my head but thanks for taking the time and effort, I have never taken the time to think about water but the other day I was filling the dogs bowl up and got a good whiff of chlorine so I checked water report this is what I get

• Summary
• Full

Analysis Typical value UK/EU limit Units
Hardness Level Soft
Hardness Clarke 1.47 Clarke
Aluminium 31.3 200 µg Al/l
Calcium 7.41 mg Ca/l
Residual chlorine - Total 0.60 mg/l
Residual chlorine - Free 0.53 mg/l
Coliform bacteria 0 0 number/100ml
Colour <0.793 20 mg/l Pt/Co scale
Conductivity 57.4 2500 uS/cm at 20oC
Copper <0.0022 2 mg Cu/l
E.coli 0 0 number/100ml
Iron <5.99 200 µg Fe/l
Lead <0.343 10 µg Pb/l
Magnesium 0.646 mg Mg/l
Manganese 1.11 50 µg Mn/l
Nitrate <1.18 50 mg NO3/l
Sodium 3.20 200 mg Na/l
This means nothing to me except Steves efforts on this made me look so thanks Steve I appreciate this a lot, what I am asking now is do I need to use campden tablets also notice we have soft water do I need to make it harder, thanks again

You have 0.5 ppm of free chlorine which is fairly typical, so it probably would be worth using Campden tablets as a precaution. Approximately half a tablet per 35L is more than enough. Crush it, stir it in, leave for a few minutes and it's ready to go.
Your calcium is very low at 7 ppm, you would almost certainly see a benefit from adding some gypsum or calcium chloride to your brews. Have a look at the beginners guide for more info :thumba:

 

[strange-steve]

@Chippy_Tea would it be possible for you to make a correction kindly pointed out by Argentum? Towards the end of post 20 could you replace this:
H⁺ = 10-2.5 = 0.0032 mol = 3.2 mg/L

With this:
H⁺ = 10^-2.5 = 0.0032 mol = 3.2 mg/L

Thanks :hat:

 

[Rodcx500z]

You have 0.5 ppm of free chlorine which is fairly typical, so it probably would be worth using Campden tablets as a precaution. Approximately half a tablet per 35L is more than enough. Crush it, stir it in, leave for a few minutes and it's ready to go.
Your calcium is very low at 7 ppm, you would almost certainly see a benefit from adding some gypsum or calcium chloride to your brews. Have a look at the beginners guide for more info :thumba:

Cheers Steve will do next brew your post is most helpful and very in depth I would never do this but your post as achieved its objective for me thanks

 

[Torshon]

It took me 3 years to realise that the tangy flavour in my beer was Chloramine! I use Campden tablets and treat all the water, best thing I ever did, beer is a hundred times better!

 

[GregH]

I RO my water but am now wondering if the flow rate is too high to get rid of any Chloramine if it has been added. I think I may add half a Campden tablet in addition to filtering for the next brew just in case.

To me I can always pick up something in the taste, no one else has ever said anything so could be my imagination.

Great write up Steve.

 

[nixhaz]

Just found this treasure trove of wisdom, thanks @strange-steve !

Just wondering if L-ascorbic acid would work the same as ascorbic acid for reducing chloramine? (I'm soooo not a chemist!). My water authority is one of the rare ones that uses chloramine not chlorine.
I've been using campden tablets up till now, but have this bag of L-ascorbic acid which I'd like to use up (bought it for work and never needed it in the end).

 

[strange-steve]

Just wondering if L-ascorbic acid would work the same as ascorbic acid for reducing chloramine? (I'm soooo not a chemist!).

I think so yes, although not being a chemist myself () I couldn't say for sure.

 

[MmmmCitra]

WOW, what an informative but slightly confusing thread, well done Steve for your time and effort.
I'm sure it's been asked before, I've probably done the asking, but, as I use Tesco Ashbeck do I really need to do much if I'm brewing a light coloured hoppy Pale or IPA ??
At the moment all I add is 1/8 tsp Gypsum & 1/2 tsp C. Chloride into boil, about 10 lts BiAB, for no other reason but it seems to work ok ish.
Also what's the difference between Chloride and Chlorine, I see there is some Chloride in the Ashbeck which is surprising, does it need a campden tablet maybe ??

Many thanks.......

 

[bobukbrewer]

Ascorbic acid—also known as L-ascorbic acid— the other form is sodium ascorbate...

 

[strange-steve]

do I really need to do much if I'm brewing a light coloured hoppy Pale or IPA ??
At the moment all I add is 1/8 tsp Gypsum & 1/2 tsp C. Chloride into boil, about 10 lts BiAB, for no other reason but it seems to work ok ish.

Not a lot really, but I would probably make a couple of small tweaks to what you're currently doing. Try increasing the gypsum to about 3/4 of a tsp per 10L and add it, and the calcium chloride, to the mash water rather than the boil. This'll give you a more typical pale ale profile, plus it'll increase the calcium to about 140ppm.

Also what's the difference between Chloride and Chlorine, I see there is some Chloride in the Ashbeck which is surprising, does it need a campden tablet maybe ??

Simply put chlorine in brewing water is bad and chloride is good. Chloride is an ionic form of chlorine and so is found as part of an ionic compound, eg sodium chloride or calcium chloride. It adds to fullness of flavour and enhances sweetness. Chlorine however, as found in tap water, is added either as elemental chlorine or as sodium hypochlorite which decomposes to release chlorine, and it reacts in unpleasant ways with compounds found in wort.

 

[MmmmCitra]

Brilliant, many thanks for this info............so i'll add more gypsum and add both to the mash keeping 1/2 tsp of CC, and there is no need for a campden tablet :)

Adding to the mash, is that right at the start when adding the grain or after the mash has finished but before the boil ???

 

[strange-steve]

Adding to the mash, is that right at the start when adding the grain or after the mash has finished but before the boil ???

Right at the start, mix the salts well into the water before you add the grains.