Making water for coffee – Part 3 – Optimising RO Water

Please note that I have a new and improved method to make water for brewing coffee here.

In the last couple of instalments, we looked at a little theory behind coffee water and then how to make up some bottled stock solutions that we can add to RO water to create a water recipe for brewing coffee.

We made 3 stock solutions one to add magnesium, one calcium and one to add alkalinity. We made separate solutions so that we could mix them up to different levels of each of the required constituents.

Recipe 1 – Calcium Only SCAA Spec Profile
In this recipe we’re adding only Calcium and Alkalinity into the RO water. We’ll be adding 2.3ml of Calcium stock solution and 1.8ml of the Bicarbonate solution to each litre of RO water. This results in a water profile as detailed below.


As you can see we’re hitting 78mg/L as CaCO3 Hardness and 40mg/L as CaCO3 Alkalinity. There is a downside to this recipe in that we are over spec on Chloride which can start to cause sourness to creep in to shots at high concentrations (although it’s suggested that this figure is much higher than those we’re hitting here).

Recipe 2 – Magnesium Only SCAA Spec Profile
His recipe is similar to recipe 1, the only difference is we’re adding Magnesium to give the same hardness, bicarb remains the same. To achieve the desired hardness we add 2.8ml of stock magnesium solution and 1.8ml of Bicarbonate solution to each litre of RO water.


Again we’re hitting 78mg/L as CaCO3 Hardness and 40mg/L as CaCO3 Alkalinity. There is a difference as we’re no longer adding Chlorides so this should be a good thing.

Recipe 3 – Fifty/Fifty
This time we’re using a profile recommended by Maxwell from Colonna & Smalls. We will add 1.7ml of Magnesium stock solution, 1.4ml of Calcium stock solution and we’re upping the Bicarbonates 2.1ml per litre of RO water.


We’re pushing the hardness up to around 95mg/L as CaCO3 and Alkalinity to 47mg/L as CaCO3. We’re also adding both Calcium and Magnesium hardness in equal amounts. The Calcium gives the resulting coffee body and creaminess and the magnesium starts adding sweetness. The water starts getting more aggressive so brew rations may need to be adjusted accordingly. We’re also balancing Chloride and Sulphates which is a good thing in the beer brewing world but I have no conclusive evidence as to its effect here.



This method is by no means perfect and I’m still working on improvements. In beer brewing there is a big focus on Temporary Hardness vs Permanent Hardness. Temporary Hardness is Calcium/Magnesium that is associated with Carbonates/Bicarbonates, Permanent Hardness is Calcium/Magnesium that is associated to Sulphates/Chlorides. In our example we’re adding Permanent Hardness which I believe is less desirable.

We are also adding in Sulphates and Chlorides which could be affecting taste and also having a negative impact on our brewing gear.

We’re adding nearly twice as much Sodium as recommended by the SCAA specs. Whilst it’s known that a small concentration enhances sweetness it’s not clear what happens when you start going beyond this limit.

Finally, the majority of these additions are Alkaline in their makeup and since RO water doesn’t really have pH as such (as there are only trace amounts of anything in there) we will almost certainly end up with water that it quite Alkaline which is not so desirable. I’ve tried adding acids (as they do in beer brewing) however this tended to result in coffee that lacks body and depth of flavour.

On the whole using this method I was able to make water that produced coffee that was more to my preference to my tap water (filtered) and also all brnds of bottled water that I could get my hands on with decent profiles. It also gave very consistent results where tap and bottled water changed quite a lot from sample to sample. This is certainly room for improvement and I’ve got some thoughts around that which I’ll explore later.

Finally, if you are interested in other recipes then post below and I’ll get them added in.

6 Comments. Leave new

  • Amazing, thank you for all your work on this!

    I’d recently been looking at Cirqua’s AB Formula and couldn’t help but think it’s a massive mark up on tiny quantities of chemicals. Unable to find a supplier here in the UK, making it myself seemed like a great idea.
    I don’t understand the chemistry, but I did note that Cirqua needs to be added in a specific order, do you know if this is the case for your formulation?

  • Spencer Webb
    July 22, 2015 4:58 pm

    Hey Ben,

    I actually have some A/B formula, I think they’ve stopped selling it now though. I picked some up whilst over in the States last year. It’s very similar to what I’m doing here, it’s basically a mixture of distilled water and Sodium Bicarb and Calcium Chloride.

    For my solution I’ve always added the Bicarb solution first, not for any particular reason though. I think the formula AB states that the two should not come into contact with each other directly rather than have to add in a certain order but it’s been a while. The reason is that if the two mix at such high concentrations then they will react and form solid compounds which is no good as you want them in solution in the water 🙂

    I’m currently working on a new post which details my latest method for creating water. The new method creates the most fantastic water for coffee, I couldn’t quite believe the difference and everyone who has tried it says the same. I’ll get the new post up as soon as I can.

  • I’m definitely interested in doing this myself – your next entry may well be closer to my capabilities of course. Good series.

    • Spencer Webb
      July 27, 2015 7:56 am

      Thanks Rob! I wouldn’t say the new method is any easier but the resulting water (thus coffee) is in a different league.

  • Nikita Barlow
    August 24, 2017 9:59 am

    Hey guys, is it imperative that I use a soda stream for making calcium waters? I’m not an expert at all but I read that calcium chloride is best soluable in water? Did you not enjoy the flavour of this in your water and also why did you choose r.o as opposed to distilled or demineralised waters ?

    • Hi Nikita,

      Soda Stream is only required if you are working with Carbonates (Calcium or Magnesium) as they are practically insoluble in regular water. Chlorides and Sulphates are soluble, however I’m not a big fan of the resulting flavours and prefer carbonates.

      I chose RO water as RO filters are relatively inexpensive when working in a home setting. Distilled water is harder to make in decent quantities and requires lots of energy so I stuck with RO. I’ve no experience with De-mineralised water so can’t really comment.


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