Water purification/filtering best practices

Hi All,

I currently live in a town where the water isn’t great and, have to find a better solution than the straight filter I have. I’d like to get some advice on good RO units (local roasters and cafes use RO in my area) that are designed for super-low scale home use only. The 250 liter/day units are overkill and basic filtering isn’t going to cut it.

I have a GS/3, Compak K8 and use a good quality but basic filter. I generally make 3 to 5 espressos (some of which have milk) per day.

Thanks in advance,


Before diving into filter recommendations, let me ask two questions:

-Why do you want to go the RO route?
-Is your model directly plumbed?

Water filtration is important for coffee and espresso, but you obviously know that already. Choosing the appropriate filtration solution is determined by a few things. Namely, do you have water impurities impacting flavor, do you have water impurities impacting machine functionality, neither, or both?

In my opinion for espresso machines, the most important thing to consider is water hardness (impacting functionality). If the water is too hard, the inside of the boiler will slowly fill up with scale until it is eventually inoperable. This is a problem. But on the flipside, if the water is too pure, the machine will struggle to function properly, and the espresso will be flat and lackluster.

The probes inside the boiler (specifically the level indicators) need conductivity to work. Pure water (a la distilled water) is actually not conductive. Also, coffee extraction is better with some minerals in the water. Here is an article that explains some of the roles of cations in extraction: http://pubs.acs.org/doi/pdf/10.1021/jf501687c

RO filtration may be detrimental to your cause if flavor is the biggest driving factor. RO removes almost everything leaving a level of minerals low enough that extraction may suffer, but you won’t get scale… Some systems offer mineral reintroduction post filtration so you can get the exact hardness and TDS you want. I would be curious to know if that is the case for the shops in your area.

If you know the hardness of the water in your area, you can make better decisions. Water test kits are cheap ($15 online).

Lastly, I would challenge you to consider your dismissal of commercial filtration if you choose to go the inline route. For less than $150 online, you can get an Everpure ESO7 filter and head. If you are willing to drop several thousand dollars for a home setup, invest a hundred to keep it in top shape!

For whatever it’s worth, we use the ESO filters at my shop. They get us in the 50 ppm hardness range which is the recommendation for my espresso machine from the manufacturer.


Hi Chris,

Thank you very much for taking the time to write that.

I’m currently using an Everpure EV9607-10 ESO 6 with my machine that’s plumbed in. The main reason I was considering RO was, again, due to all the shops in the area using it due to the water quality. I was expecting to be getting an RO unit that included mineral replacement. I’m not thinking of doing that without getting my water tested but, wanted to explore available options.

The EV9607 was recommended to me when I was living in Salt Lake City by the local espresso repair shop. The shop that I use in San Diego has close ties to La Marzocco so, their recommendation seems like something I should take on board. I was really just hoping that I could get something that wasn’t $1200, just looking to see what other units may meet my needs.

As another data point, when my machine came back from the shop, it still had water in it, which tasted better than after it’d been home for a little while.

Thanks again for your help,

Does your machine still taste better now that it’s been home for a while? I would be curious to know if some other aspect of the repair may have impacted flavor quality or if it was the psychological factor or if it was indeed the water.

For me, frame of mind is probably the most important variable when it comes to coffee evaluation. Am I excited going in? Do I know what I am ‘supposed’ to taste? Am I distracted from the coffee (working on the computer, getting ready for work, etc…)? Am I specifically evaluation something?

I find that if I am tasting something specifically for the purpose of evaluation, I enjoy it 5X than if I just drank it because I wanted something. So basically where I am going with that is that ruling out the psychological impact of testing the repairs of my beloved espresso machine after having been without it for a time would make unbiased evaluation nearly impossible (for me). Just something to consider…

As for which filter to get, what is the primary issue with the water in your area? You may find a water assay by just Google searching it. Here’s one from in my area: https://www.hsvutil.org/ac/wp-content/uploads/2015/05/Huntsville-CCR-3-27-15.pdf

So the answer is, it depends! What are your filtration needs?

1 Like

For so few espressos I would buy distilled water and remineralise manually. You’ll be nailing the quality, and winning on wastage (zero)


newbie question, how do you remineralise manually? I have heard about adding potassium carbonate to distilled water…

Here’s a good start, Josh!


I think it’s difficult to have a useful, and reusable conversation when the answer is “it depends”. I get that’s often actually the best answer but it doesn’t help a whole lot. “It depends” is good best practices discussion but, I was hoping to get some specific advice around units - i.e. delve into the practical as well as the theoretical.

I can’t imagine that I’m the only home user with nice gear who’d like to work out what a good solution would look like. The solution proposed to me by the local shop is “buy this $1200 RO unit” so, I phrased my actual question in that light. Is there a good RO unit I can get that would be cheaper given the very low throughput a home user will generally have. LM have an RO unit in the EU but, from what I’ve heard, that’s not going to be released in the US.

I hope I’m not belaboring the point. Thanks to Alex for the link, still getting through those videos.

I’m leaning more towards RO with mineral replacement to account for variable water without the potential overhead (yes, I’m lazy) to manually doing mineral replacement. My espresso machine is plumbed and I’d like to keep it that way if possible.

I’m a home user. Only pull 2 or 3 shots per day. I mix distilled with my tap water, roughly 50/50. But it depends on your local tap water quality. This low frills arrangement works well for me.

1 Like

I am not an espresso guy, but I would throw this point out there.

Given the extremely short extraction time, this is mainly a physical rather than chemical process unlike coffee brewing. Hence, I have read that using distilled water through an espresso machine is actually preferable from a machine maintenance view and does not subtract from the flavor profile, adds predictability.

I don’t know, since I make my own water using Zero filtration and Global Customized Water home pak(125ml) for mixing to the targeted ppm. It is a really, really neat option from them particularly for home use.

Howdy Daniel! I purchase RO units every few years (near their longevity due to plastic deterioration), and select the best featured units at a value price. Examples are usually 5 or 6 stage, usually from 75 to 100 gallons per day, with the final stage specific to your needs. I wanted additinal metals cleaned from my tap water, so I have ordered a RO/DI system with a De-ionizing silica beads final stage:
Then one could simply add a seventh stage for mineral replacement:

or purchase a system that has re-mineral stage in the package: (sometimes referred to as ‘alkaline’ systems)
There are also kits to add sterilization:

if that may be a concern in your area. Often your city/county water department website will have a bunch of data compiled for you about or local water supply, and it will assist you in deciding what you want to remove, kill, or replace. :slight_smile:
As Matt suggested earlier, an RO does waste some water making clean water (usually less than 2:1) and filters need servicing when required. I use this TDS meter to instantly measure input and output, and calculate efficiency:

from any online RO efficiency calculator, like:

If coffee is the ONLY thing you need RO water for, it would be more convenient to go with Matt and others suggestions, but I use my RO water for everything: cooking, drinks, cleaning,etc. and haven’t been without an RO unit since the mid 70’s. Oy! Cheers!


It is most definitely a chemical process. Distilled water in an espresso machine makes overly acidic, unbalanced and low-texture shots. It can also severely damage your espresso machine!

You will be screwing around with an RO for hours and hours, possibly weekly, to get any kind of consistency out of it.

I strongly recommend the manual remineralisation. Read the water book, make a ghetto recipe with bicarb and epsom salts. Weigh them out into one big batch and seal it into zip lock bags in batches perfect for each bottle of distilled water you buy.

You will be spending nothing compared to RO, and it’ll always be the same. RO is not a magic bullet, and often makes water taste worse. :slight_smile:

1 Like

As Matt mentioned, your temperature probes actually need minerals in the water to conduct electricity and function properly. And out of control temperature is not the sort of thing you want happening inside your very expensive machine!

Hello all,

You really need to consider two major factors. Carbonate Hardensss (this influxes PH and balances water) and General Hardness (this does the extracting, it’s is mainly composed of calcium and magnesium in the case of coffee). TDS or total conductivity is a useless measurement unless you are over the 400ppm range.

Relationship between KH (carbonate hardness) and GH (general hardness) is key. Too much KH your coffee tastes flat and tasteless, not enough and your coffee is over sharp and sour. Too much GH your coffee tastes heavy and chalky, not enough and it is uninteresting and dry. You need to know what the relationship is in your water to correctly choose water treatment. Gone are the days of TDS meaning anything when we talk about water.

RO. They do one thing, they linealy drop total conductivity with no change to mineral content. This means if your KH and GH are in the wrong proportions this may not be the best solution.

Softners. They reduce hardness. Not as much as an RO.

Ion Exchange. This is super clever, it changes the minerals in your water. I.e swaps calcium for magnesium and KH for GH. This doesn’t change your total conductivity though so that needs to be right first.

Check out Maxwell Colonna Dashwood and Cristopher Hendons book water for coffee they go into more depth.

Hope this helps!


Lots of initial fiddling, and learning the how’s and why’s certain filtration/purification elements are involved, but once set up, the output is HIGHLY consistent. So much more than my tap input, which is subject to either shallow or deepwell supplies selected by my water district and varying solute concentrations as the ‘water season’ supplies progresses. Towards the end of summer, most locals simply can no longer drink from the tap. At 90% efficiency, time for filters, badabing…consistency. An EPA ‘Superfund’ site (herbicide factory dumping for over 30 years) less than a mile away got my ball rolling back in the day. I was more focused on ‘purification’ (OP’s title) than taste, but I think RO is an excellent STARTING POINT (not a magic bullet) if the hardness and pH of supply is in range…simply adjust final stage, either by cartridge of manually. Yes, one can still get there by buying distilled and doing the work…and if the hardness and pH of supply are not conducive to RO, then perhaps a home distiller would be a simple and reliable solution. :slight_smile:

I believe distilled water alone lacks conductivity for the refill probe, but it has never been a problem with my amended RO water (nor my RO water alone). Some machines may be more fussy than others, however. Don’t believe I’ve heard it affecting temperature stability before.

I would add two more: pH and source of supply. They go hand in hand…deep well, shallow well or surface waters all have disparate inputs before arriving at your tap. I disagree that TDS is useless/meaningless…it’s an important metric when discussing ‘purification’. I also disagree RO’s do ‘one thing’…they do many stages, and most certainly alter mineral content and pH. The first stage spun poly sediment filter itself dramatically drops the iron content, as well as the stages after it, for example. Here’s a list:

@Alex Absolutely! I was speaking specifically of distilled water. Thanks for aharing all the helpful resources and info on RO.

I have used the “ghetto” recipe, for about 4 months, for brewing and this really pulled fruitiness and body into the coffee. The only problem I had, was that a distinct “mineral” taste began to develop in my hario kettle even though no deposits were to be found.

I eventually used CLR around 10 repeated cycles, to evenutally clear out the mineral taste, not sure how/why that occurred.

Still not sure how distilled water can damage a machine :slight_smile: but will read up. Just for predictability, I use Zero water and the 125ml kit from GCW. I need to understand now how to adjust PH from that 100pm baseline.

BTW, your V60 01 youtube video started me down this slippery path :smiley: