Coffee

Just use vinegar.

Anytime you're talking about scaling due to hard water, just use vinegar.

Even with a dishwasher, throw an upright bowl in there with some vinegar.

There might be some special products that work a teeny bit better, but they don't cost a dollar for a gallon.

All you need is the acidity. Descaling happens by the acid neutralizing the alkaline scale, which is calcium based, and turning it into its salt form which is water soluble. Any acid will work. You just need enough molar quantity of it to react with however much scale is in your machine.

Citric acid works. Acetic acid (vinegar) works. Carbonic acid would probably work... Hydrochloric, sulfiric, or nitric acid would work too, but would be a monumentally bad idea.

Just use some vinegar or citric acid in water. There's no need to pay more for fancy descaling products. I have a ~$6000 Miele coffee machine. It came with a few of its fancy cleaning and descaling tablets. When I ran out of those, I just started using bulk citric acid in the thing, bought in multi-pound quantity from the internet. Two pounds of the stuff is like 10 bucks, and will probably last you the rest of your life. For reference, my machine reports that it has dispensed about 8000 cups of coffee in its little report doohickey and the generic citric acid dissolved in water works just as well as the fancy Miele branded tablets that are $22 a pack.

Everyone else is saying vinegar, which will certainly work.
But if you're like me and cannot stand the stench of vinegar, then I recommend citric acid. 2 tablespoons to a liter of water is a good place to start, but you can most likely find dosage specific to your machine with some googling.
Also, you can get ~2kg of citric acid for 15~25 $or€. I use it to descale everything from coffee contraptions, to shower heads; and a big bag of it lasts us 1½ years. Our water is fairly hard too, about 160 TDS.

Note that citric acid works a bit more nuanced than many other descalers: it acts as a chelating agent at high concentrations (2x the Ca2+ concentration) and is more effective at removing scale because of this effect, but at lower concentrations the effect might actually be reversed because it can form solid calcium citrate, which has a very low solubility in water.

If you are using citric acid based descaler you should make sure that you are always using enough of it to avoid the formation of calcium citrate.

Thank you all, i think ill start using citric acid or vinegar since I have them already. I was hoping its that simple, but still needed your answers. Cheers ☕

Commercial descaling solutions often contain perfumes and coloring agents. These can linger in your coffee maker. Do not use them for your coffee maker.
Just use plain old vinegar. Run it through, let it soak for a couple of hours (or overnight). Rinse thoroughly a couple of times and you should not have any remaining acidic smell or taste.

I'll echo everyone else and say vinegar for sure. A gallon of vinegar is a few bucks at worst.

Anymore, though, I buy distilled water for my coffee maker. It eliminates the possibility of scale. I use 750 mL when I make my coffee and a gallon of distilled isn't even a dollar. It's still a good idea to run some vinegar and water through it every once in a while because vinegar kills mold.

Here are some other vinegar uses for those who don't have much use for vinegar:

Will emphasize what's already being said about food grade white vinegar. However, I'll put a plug in for a Reverse osmosis system. No longer super expensive and filters last years. Pretty much eliminates scaling but more importantly you are going to get a better tasting brew. Excellent daily drinking water too.

For products like this, look at the ingredients list and figure out what each one is for. Then make your own, and leave out the shit you don't need, like scent.

For coffee makers, citric acid or vinegar as has been suggested are both good options.

Another approach:

Could you just use one of those brita pitchers that purify the water? (Just use it for your espresso maker)

https://www.brita.com/water-pitchers/

I think their filters contain water softeners.