Possibility to measure water hardness

Hi folks,
Don't know what I did wrong in my previous life, but it must be something very bad...

Got LOTs of troubles with my heating system last week, and seems a lot of it was caused because my water descaler device (not sure if that is the correct english translation...) also is failing partly. Which I also didn't notice. Me getting completely nuts at the moment :exploding_head:

Ok, so here is my next water related noob question. Are there decent affordable sensors to measure water hardness in some way (e.g. via a wemos d1 mini)? And I don't mean something manually, because I would forget it again for sure... I mean automatic measurements at regular intervals from Node-RED.

I see for example this project, but not sure if it is useful for my purpose. And I will not be able to mount such a sensor in my water pipes, since it is for swimming pools.


Bart, as far as I know, water hardness is measured chemically. I don't believe there are instrumental methods.

Where in the system is the descaler? Usually the water in heating system itself does not change so the heating side of it doesn't scale up. Provided an inhibitor has been added when it was filled there would not normally be a problem.

Hey colin,
I had not only troubles with heating but also with the warm/hot water that we use. About 8 valves where defect due to hard water. Valves that we normally only need to use when things need to be replaced, and that was now the case...

Hi Garry,
I was afraid that that would be the answer. I do it like that currently, which is the reason I often forget to do it...

OK, understood.

Isn't it pH that you need to measure? Google tells me that there are lots of pH probes available, but I know nothing about them.

That’s how: (I use this for my pond and always feel like when I was young and producing black powder with my sisters chemistry kit)

Or ask your local water supplier. The hardness is unlikely to change so it’s enough to measure it once and you can't do a lot against it unless you spent a lot of money into reverse osmosis. Don’t fall for all the magnetic coil voodoo scams: The truth about electromagnetic water treatment! (PWJ193) - YouTube

My parents had a reverse osmosis device. It was as big as a medium fridge and eating a ton of salt and energy. But made really soft water. You could feel it (a little bit like there is a tiny bit of soap in the water) cleaning windows is easier too.

There are smaller devices available for drinking water only (and for your plants) - perhaps you can fill your heating circuit too as it is a closed cycle.

Or by some ? canisters of demineralized water. The only issue might be how to fill it in your system up to 2 Bar above normal pressure.

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I was wondering the same today. In contradiction to @Christian-Me, I only have one little bottle. It is becoming a habit that he has everything multiplied by 20 at least :wink:

The guy from my water descaler device has just passed by, and he also was not aware of any sensors... And he confirmed that measuring the pH was not enough.

Well this (and others) suggest that pH is a measure of hardness. Whether that is the same the likelihood of causing scale may be another matter. What does your little bottle say it is measuring?

pH Levels in Drinking Water - ATS Environmental.

It sounds very charming when you say it like that. Thanks for chearing me up :wink:

If I understood the guy correctly, then I am now measuring Calcium and Magnesium ions. While a pH measurement does measure the Hydrogen ions...

Not really @Colin.

Typically hardness is treated using a water softener, which exchanges calcium & magnesium with sodium. These devices require salt to be replenished periodically. If this is the type of device you have, then maybe there is a controller that can monitor salt levels. You might be able to take it a step further and monitor water usage and estimate the amount of salt being consumed. Or, maybe there's a way to measure salt in the post treated water:

My understanding is that "descalers" advertised for residential use don't really soften the water, but claim to cause the calcium to "clump" into larger particles that pass thru the pipe and down the drain. I'm not sure I believe that.

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There is even more in the box (I bought if to take care of my :seedling: and :tropical_fish: ) but the biological filter (two extra ponds) does such a good job I only use it once a year in spring to check the critical phase when the algae are faster growing than the plants.

But in general carbon hardness and total hardness are the key factors to your problem.

You can buy test sticks. They usually come with your dishwasher to be able to adjust the reverse osmosis device build in. And good to know to get the right dose of the washing powder

For my pond I need Iron (plants) nitrate, amonium, nitrite … but to be honest nice to know the values but with 80qm there is little you can do if the values are bad. Only exchange the water. But a good feeling that everything if in best order since the beginning the fish are happy, the Dog only likes to drink pond water (perhaps the best indicator as he refuses to drink tab water)

And I tested that the water filters really work and bring the hardness significantly down (as you can also see in your cup of tee)

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What is that? Interesting :face_with_monocle: just curious how this works (or even not)

My parents had something similar to this

As far as I know they exchanges the calcium and magnesium with Natrium.
The calcium chlorine (or so) is then drained. You you need 100kg salt per year and waste 8.500qm water and 28kWh (says the charming guy on his website)

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That was the word I was looking for. Thanks for expanding my English vocabulary!

Yes exactly. I perhaps should have mentioned that in my original question. Was not thinking about the existance of other types. My bad...

Well the salt is tablets that you have to fill every few months in bags, so that is not easy to estimate. But measuring salt in the post threated water might indeed a way to go. Although I don't fully know the process 100%, it somehow makes absolutely sense what you are saying. Thanks for sharing your thoughts!!!

My God Chris...
Although I am now starting to doubt that your real name is Chris...
Are you a former spy on the way to eliminate a victim?
From now on I am not going to contradict you anymore :cold_face:

Yes something similar. Have tried lots of years without, but the water in our region has a very high hardness (which is done deliberately by the water company), so had no other choice than buying one.

I am not sure what I am missing then. From the link I posted:

How Does The pH Determine If My Water Is Hard Or Soft?

Water is considered soft as the level drops toward the lower side of 6.5 and out of the recommended range.
Water is considered hard when the pH level is above 8.5.

Wait a moment …
I should still have one of the family toys in the attic…
One moment please …

Here it is:


Colin, that is just not true!
Before I retired I worked in textiles for over 40 years as a textile technician. One of my responsibilities was ensuring that our pH equipment was functioning properly, and procuring suitable electrodes and instruments.
There is no simple instrumental method to measure hardness, you have to use chemical analysis.
Water is acidic below pH7 and alkaline above pH7.
There is a relationship between water hardness an pH, but in no way as simple as you posted.

I searched earlier for "Hardness pH" and this came up as the first result:

" Scientists measure the hardness of water using a pH scale , which measures the hydrogen-ion concentration in the liquid. Water with a low pH is more acidic, while water with a higher pH is harder or more alkaline, meaning it is able to neutralize acids."

This is a load of Bo***cks. So much false information!!

OK, so I was correct when I said that the link, and others, suggested that there is a simple relation, but unfortunately the links themselves contain false information.


Yes, apologies for my rant. There is so much false information out there, even from supposedly "Informed" sources, and people go down rabbit holes because of it.
I'm taking my pills as we speak! :slight_smile: Ommmmmmmmmm.