Water For Coffee - Where Do I Start?

Yes, I know, you think water is water. Drink a sip of tap water, then a sip of RO water and tell me if you notice a difference.

With coffee being 98% water and tens of thousands of dollars being spent on any given coffee shop setup where they're serious about making good coffee, it seems pretty important to make sure the largest ingredient by volume is dialed in.

My focus in this series applies to water for cafes, which basically means water at scale (no dripping minerals into a cup at a time for me). We'll talk about how to treat water at scale in the next few posts, but for now we'll focus on giving you a starting point on your "water for coffee" map, and it doesn't matter if you're Starbucks or Sam on the corner, the basics of testing remain the same.

Start By Testing

Now, it's tempting to just buy a packet of minerals for coffee, dump it into your tap water and call it good enough. That's a lot like filling out all the answers in a multiple choice test, then going back and studying for the test. You want to know what you're doing first.

In order to get the right water recipe, you need two things. One is relatively expensive and complicated (but fun), and the other was installed into you more or less at inception.

$50,000 In Your Mouth

We'll start with the free thing: Your tongue.

Your tongue begins to develop by the 4th week of intrauterine life, and is only preceded in senses by your sense of touch.

It is an exquisite apparatus, able to taste the difference at the molecular level between things that differ by just one ion, and taste concentrations of some substances (bitter compounds like Bitrex) as low as 10 parts per billion. Yes, with a b.

It boggles the mind to realize that each of us is born with this ability to sense this minutely, especially when you realize that to replicate what your tongue does requires a liquid chromatography-mass spectrometry system.

Those start at $50,000, and they'll never give you the enjoyment of tasting the thing.

What Matters When Selling Coffee?

At the end of the day, all of the things we do to the coffee we sell are guided by our customer's taste.

Without going into the thousands of taste buds on your tongue, each of which has 50-150 taste receptor cells, or the effect on taste from what you smell, or how even your digestive tract (after you swallow) can affect your taste, your takeaway as a coffee seller should be something like:

• Customers can taste your coffee, and they know what they like.
• Making coffee that tastes good to most people is a repeatable act.

The Italians (who invented espresso) break down a perfect espresso into the 4 Ms:

• Macchina (The machine)
• Macinazione (The grind)
• Miscela (The beans or blend of beans)
• Mano (The skill of the barista, the "hand")

Being Italian, they blew right past a thing that didn't start with M and probably laughed about it while tossing back an exquisite espresso, but Water is clearly the fifth pillar of espresso.

Perhaps we can add that 5th M for Matrice (The Matrix), which is the medium in which all the other Ms exist.

How Should We Make Excellent Water For Coffee?

Before we start to build a water recipe for our coffee, we need to know some water basics. While there is a ton about water for coffee on the web, I think most of it goes too deep, too quickly, so I wanted to start with the basics in order for anyone to get a good feel for this.

Essential Elements of Water For Coffee

Water has four main elements you should pay attention to:

• pH - The Corrosion Factor. While pH matters for taste, its main impact is on your coffee machine. Too acidic and it'll eat your boiler, too basic and you'll have to deal with buildup.
• Hardness - The Flavor Extractor. Think of hardness as magnets pulling out the flavor from coffee. We'll use Magnesium to accentuate fruitiness and acidity and Calcium to provide creamy mouthfeel and body. The ratio of those is important, and unlike other things in this article, overkill on either of these is a real problem.
• Alkalinity (confusingly, not the same as pH) - The Acid Buffer. Alkalinity creates a buffer zone for your pH, allowing you to play a bit more with acid without accidentally going off the rails. Think of it a bit like a sponge for acid. Soak up too much and your beans can taste flat. Soak up too little and your coffee will be sharp and vinegary.
• TDS (Total Dissolved Solids), or how much stuff is in the water. TDS is a rough guide; it'll tell you if there's a problem with your filtration system ("Hey, TDS is climbing, you should replace your cartridges"), but it won't tell you if your coffee will taste good or bad.

We'll deal with other taste-killers like chlorine (I grew up swimming in chlorine pools, and while they're fantastic for keeping the water clear, chlorine does nothing good for coffee).

Now that you have the 4 dimensions, let's go through how you can test them.

Testing Water for Coffee

Trust me, you can get WAY in the weeds with building a water recipe (and for some of us, that's fun), but starting with a recipe before you know what's in your water is like walking in 10' high elephant grass; you'll have no idea which way to go because you don't know where you are.

Let's put a pin in the map first, and test each dimension.

We'll start by testing our "raw" water source: What you get from the tap. Later we'll get into how to check if your RO or other filtration methods are working, but let's start at the very beginning.

Testing Philosophy

One job of a business is to be obsessed about something that isn't worth being obsessed about for a normal person. That's how I am with testing water. There is no reason for you to use the same tools I've invested in; you can probably spend 1/10th as much and get usable results.

If you read this and think, "Nik, there's no bloody way I'm spending $5k just to test alkalinity and hardness in under 7 minutes", that's fine. You don't have to.

What IS important is knowing what to test and what to look for. How much money you spend doing that is relatively unimportant in getting good-enough results to run a much better than average coffee shop.

Your city will give you its results for free. For example, in San Diego (where we have 3 water processing plants), the Alvarado plant that serves Paleo Treats produces water that has the following:

Measurement	Value
TDS (Total Dissolved Solids)	479 ppm
Total Hardness	216 ppm
Alkalinity (Total as CaCO3)	116 ppm
pH	8.3 (range: 7.7–8.68)

That's awesome, but I'm with Reagan when it comes to the water I'm drinking: Trust, but verify.

Oh, you could also skip testing your water yourself and just send it off to a testing lab where they'll use ultra fancy gear and give you a fantastic snapshot of what your water was like the day you tested it.

Now that we have the "How you can test" options laid out, I'll assume you want to test things yourself.

Testing Water pH

You can use a bunch of different tools to test pH, from adding special test droplets to your water that give you a static color match ("This shade of green equals pH 7") to dipping in strips of paper and eyeing the color change to going all-in batshit crazy and using lab-grade equipment to measure the electrical potential difference between a pH-sensitive electrode and a reference electrode while compensating for temperature.

Yes, of course I went the batshit-crazy route with an Oakton PC700 and WD-35641-51 pH Electrode, but you don't have to.

A quick note here (if you ignored my advice to start with your tap water and just thought to yourself, "I'ma jump ahead of Nik and test my RO water first"). RO (and distilled water) is difficult to get a solid pH reading on without sophisticated tools and time.

This is because pH is a measure of hydrogen ion activity (H⁺) in solution. The more activity and concentration, the easier it is to measure. If you have super clean water with very limited activity and concentration, there aren't enough data points for your testing probe to get you an accurate reading without waiting a long time and sampling a lot of water.

It's kind of like having a map with a giant "Here Be Dragons" blank space on it. When you step into that space, it's hard to know where you are without any reference points.

Start with sampling your tap water so you know your starting point.

The San Diego report suggests I should have a pH of 7.7 to 8.68, and I measured it at 8.12 on April 16th, 2026.

Testing Water Hardness

Once you have that first pin of pH in the map, move on to water hardness. It doesn't really matter in which order you do these tests, but this is the order I've done 'em in.

Water hardness is the "extraction engine" of your coffee. It's primarily a combination of Calcium and Magnesium. When you test water hardness, you're actually testing the total sum of both Calcium and Magnesium.

Splitting the two into separate measurements is costly and difficult, and for initial testing, the "total" water hardness, also called GH for General Hardness, is enough information to build a recipe on.

Calcium and Magnesium pull different flavors out of the grind and into the water.

• Magnesium: Magnesium pulls out the sharp, fruity, and acidic notes in light-roast coffee. It binds strongly to the flavorful acids in the bean, and has the additional benefit of being less prone to form scale, which will clog up your machine.
• Calcium: Calcium is what gives coffee "body" and that creamy, heavy mouthfeel. It's the traditional "hardness" found in most tap water. However, Calcium is the primary ingredient in limescale. When heated in your espresso boiler, calcium drops out of the water and turns into stone.

We'll talk more about building your water recipe after we figure out what's in your water, but for now, you can't just dump in a shitload of both Calcium and Magnesium; this is not a case of "when in doubt, overload."

Water Hardness Testing Kit

Water hardness is usually tested with a water hardness testing kit.

You get a bunch of different chemicals in the kit, you add drops of 'em to the water you're testing, and when the water changes color you have a measure of your hardness.

That should run you about $35 for a water hardness test kit, and if you want to maintain tighter control of your drops, another $70-100 for a burette setup.

A burette just allows you precise control of your drops. You're still responsible for using your eyes to assess when the color changes.

Dial Up The Intensity Meter

Of course, you know we're not going to settle for strips or drips, right? If you want to go full Captain Insane-o on testing water hardness, you basically have no choice but to pick up a Hach SL1000.

I should be clear: You shouldn't do this. There's no good reason to for most cafe owners and certainly not for home testers. It is a ridiculously expensive way to overkill your way to hardness excellence.

However, the path of overkill has long been a joyous and productive one for me, so I picked up a Hach SL1000 and got to work.

The Hach SL1000 has a few advantages.

First, if you're using drops and waiting for a color change, even if you're using a burette, you're limited in accuracy to the drop size. Many titration kits assume each drop represents 1 gpg (grain per gallon). This means the drop-to-drop change can conceal a difference of up to 17 ppm (parts per million) of hardness.

A swing of 20 ppm can be enough to move your coffee's taste from vibrant to dull, so there's a potential significant penalty here, however...

You also have your tongue to guide you, so don't get too wrapped around the axle with this. The burette & drops method will get you damn close, and certainly a lot closer than just guessing.

The Hach works by colorimetry, shining a light through a strip (called a Chemkey) that you insert into it to get a precise reading. This makes it significantly more accurate than the human eye, detecting changes as small as 1 or 2 ppm.

You're not guessing "Hey, is that pink, or light pink?" with a Hach, but you could also buy a used Honda Civic for your daughter's high school runabout instead of being a bonkers-crazy water nerd.

Second, a Hach can run multiple tests in parallel, saving time when testing water.

The downside of the Hach is that it's easily fooled by cloudy or tinted water, so you can't test coffee with it, but...we're not testing coffee. We're testing water.

Should You Buy A Hach SL1000?

Now, is the Hach SL1000 that big of a deal? No. They're expensive to purchase, the strips are expensive to buy (each full test runs about $15 just in consumables for one source), and the accuracy difference will only matter for a small minority of your customers.

Water testing tip: Don't buy a Hach SL1000, and don't bother with the burette, just use the Hach kit.

On the 16th of April, when I tested hardness on my Hach SL1000, I got 239 ppm, which is close to the 216 ppm that San Diego water report gives.

216 ppm is very hard water (anything over 120 ppm is considered hard), and is a reflection of our source (the Colorado River and Northern California). We'll talk later about how this guides our treatment of the water for our machine, but for now we're just getting pins in the map.

About That Alkalinity

One of the first confusing things about alkalinity is that "alkalinity" and "alkaline" refer to different things.

Alkalinity is a measure of water's ability to neutralize acid; it's the buffering capacity of your water to handle acid.

Alkaline just means anything with a pH above 7.0.

We're going to focus on alkalinity. I said earlier to think of alkalinity as a sponge for soaking up acid, and it's worth expanding that metaphor a bit here.

If your sponge is super wet, it can't soak up a bunch more. If it's just slightly damp, it can soak up a shitload. Alkalinity has more effect on the taste of your water than any other dimension listed (although they all matter), so measuring the alkalinity of your water is critical.

It's a little more expensive than measuring hardness, usually just under $100. Alkalinity measurements are in "KH" ppm. KH stands for Karbonathärte (Carbonate) Hardness.

I use the Hach SL1000 mentioned above, but the kits are excellent.

We're not aiming for a specific alkalinity yet, we just want to see where we are. Here in San Diego, the water coming out of the tap is 118 ppm, which aligns with their report of 116 ppm.

One nitpicky nerd thing to note is that alkalinity can be measured in a few ways; we're using the "total as CaCO3" measured in ppm for this. You may see others use dKH (German degrees) or break it down into Bicarbonate vs Carbonate.

When we use the "as CaCO3" standard, we're basically converting everything into a common chemical "currency" so we can compare water recipes around the world without needing a chemistry degree.

If you order a water report, you'll probably see P-Alkalinity (phenolphthalein) and M-Alkalinity (methyl-orange) as well. P-Alkalinity is limited to pH of 8.3 or higher, and for coffee, the M-Alkalinity is what we care about since it represents the full buffer capacity.

TDS: The Rough Guide

We'll finish our testing with TDS, or Total Dissolved Solids. TDS is a way to see how much stuff is in the water. We do this by measuring the conductivity of the water, which is basically a measurement of how easily a charge can travel through it.

Note: TDS meters don't actually count the solids in the water, they measure the conductivity of the water and then guess at TDS using a conversion factor. That's why you can get different measurements of TDS for water with table salt (Sodium Chloride) vs water with the same amount of Magnesium Sulfate. The weight of the solids is the same, but the two molecules conduct electricity differently.

You can use commonly available TDS meters (as cheap as $10) to measure your tap water. In the coffee world you'll see these everywhere.

Confusingly, you'll measure Brew TDS with refractometry; you can't do that with a cheap TDS meter. We'll get into measuring your coffee in another post.

I use a dedicated electrode with my Oakton PC700 to get significantly more accurate results (the electrode includes a dedicated high quality thermistor and a more sophisticated algorithm that normalizes to exactly 25°C, which is the global lab standard for reporting conductivity) than a cheap meter pen.

To be clear (no pun intended), that's still testing overkill.

San Diego's report suggests I should have TDS of 479 ppm, and I measured 461 ppm.

Your Water Map

Now we have a good map of the territory for our tap water, and we verified it. I'll talk about how to treat water in the next post, but if you've gotten this far you're about 1,000% further than most coffee drinkers go.

Onward!