What is Water Hardness & What Causes It?

Water hardness is simply a measure of dissolved minerals in your water. The most common are calcium carbonate (CaCO3) and magnesium carbonate (MgCO3).  Rainwater is inherently soft but if it encounters limestone or chalk as it seeps into the ground, it can dissolve some of the rock which is made up of those minerals. The rate of dissolution is even greater if the pH of the rainwater is high (acid rain dissolves limestone even more). 

Is Hard Water Safe to Drink?

Hard water is safe to drink and houses with water softeners have separate taps for hard water which can be used for cooking and drinking.

In areas of very hard water, the precipitation of dissolved minerals can be a problem. The most obvious signs are the unsightly marks you see on glassware and cutlery after air drying. Over time, these minerals can also clog your plumbing causing dishwashers, toilets, coffee makers, and so on to eventually fail. The most common way to prevent this is to have a water softener that removes these minerals.

Hard Water Scale

Hard water precipitates are what you get when you forget to replenish the water softener salt. They usually show up just before that important party or dinner.

How Hard is My Water?

Water hardness test strips can determine how much dissolved mineral you have in your water. The video below shows how easy it is with Indigo Water Hardness Test Strips.

Coffee Taste & Brewing

If you’re a coffee aficionado, you have an opinion on what good coffee tastes like & what makes it so. For some, the fineness of the grind or darkness of the roast is key. For others, it’s how you brew it that matters be that French press, vacuum, drip, or espresso.

There are some who swear that it all comes down to the water. In particular, the amount of dissolved minerals. Here is what one of our customers, Brendan Pasquini of CA, who makes espresso machines has to say on the matter:

Hard Water Bad for Espresso Machines

“I just want to say you guys make a great product and your strips have already saved many a customer’s machines. As for water quality, here is the deal. Some people swear that you need minerals in the water to get a good extraction and flavor from your coffee and that soft water ruins the flavor. That may or may not be true but in all honesty the amount of people I have met in real life that can taste the difference between a shot made with mineral water with high calcium (Arrowhead) and a shot made with distilled water is 0.

A lot of people don’t realize that you can just remove the calcium carbonate without removing the other minerals. The water softener we sell only removes calcium carbonate but leaves in other minerals for taste. Most people just assume soft means R/O [reverse osmosis] water or distilled which is void of minerals. For the very small percentage of people that claim to be able to taste the difference and say don’t use soft water, my main argument is such. What tastes better, espresso made with soft water or no espresso at all because your valve is clogged with calcium?

So, in my professional opinion water quality doesn’t really affect the taste that much (if it does the people who can taste it are a small batch) what it affects is the performance and life span of your machine. That is why water is so important. ”

In other words, don’t run hard water through the espresso machine because you will eventually destroy it!

Test Calcium Levels in Milk

You can use hard water test strips to measure the amount of calcium in milk. This is not a standard method in the dairy industry but we’ve had people in the horse racing business use them to test calcium levels in mare’s milk.

Milk is an emulsion made up of water, phospholipids, proteins, and so on and the test strips will detect less than 10% of the actual calcium present. However, if you dilute cow’s milk with deionized or distilled water, you can make relatively accurate measurements.

A chemist we know did this on cow’s milk with 1.5% fat content. When she tried the test strips on the undiluted milk, she got values of approximately 100ppm (the nutrition label indicated 120mg/L or 1200ppm). The results using 3 different dilutions are shown below.

DescriptionOur SKUOur Price USDBQ SKUBQ Price
#5 watchmaker ("swiss style")224905.9545359.71
#7 watchmaker ("swiss style")224935.9545328.42
splinter forceps, straight224162.9547314.54
splinter forceps, curved224202.9547324.54
medium point forceps, straight224252.9547344.61
dressing forceps 125mm/5"224302.9547354.68
10"/250mm thumb forceps ("long")224585.95473016.13
12"/300mm thumb forceps ("long"))224597.95472917.14
iris scissors, straight ("dissecting")222083.9547137.12
iris scissors, curved ("dissecting")222103.9547147.12
microdissecting scissors ("iris")2222113.95471529.8
5X/5X loupe, <30mm glass ,
(19mm plastic) lenses
10X doublet small (17 vs 12mm)23220-104.351129A13.1
10X doublet large (23 vs 20mm)23223-1012.951128B42.8
10X triplet (21 vs 18mm)23231-1018.951129D59.79
20X triplet (21 vs 19mm lens)23231-2020.951129X18.63
6X linen tester, 25mm ("4X", 1")234129.951129Z23.66
Minutens 0.15mm (NEW)33416-1524.251208SA24.83
Minutens 0.20mm (NEW)33416-2024.251208SB24.83

If you go to the USDA site & search for milk, eg. 3.5%, whole, etc. You can see they have different calcium levels but 125mg per 100ml (1250ppm) is a typical value.


  1. The US Geological Service: Water Hardness by Zip Code
  2. A water softener company compiled this: Water Hardness by Province in Canada.
  3. If you are really a coffee fiend, read about: Coffee and Water.
  4. Calcium levels of almost any US brand of milk: USDA Nutrient Guide.

For the Hard Core Coffee Fiend

If you know a serious coffee drinker who’s hard to buy for or simply likes gag gifts, we offer an assembled molecular model of caffeine.

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