# TDS readings a hard or soft measurement



## joshvito (Apr 6, 2009)

If this is in the wrong section of the forum, I apologise. I could not find a "Chemistry" section.

I understand that Total Dissolved Solids is a measurement of "all combined content of all inorganic and organic substances contained"* in water.

What I would like to know is if my water is hard or soft depending on my reading on the TDS meter.
I am pretty sure I have hard water like every other western new york-er, but I would like to know how hard.

What is the average TDS in the Amazon River basin?
What is the average TDS in Lake Tanganyika?
At what reading does soft water become hard water?

What I would like to have is a TDS number to try and match to get my 130ppm tap water softened enough to be considered "soft water".

I am also wondering if hard water has correlation to CO2 solubility.
If it is too hard, does it prevent the CO2 from dissolving to desired concentrations?

Thanks for any information.


* http://en.wikipedia.org/wiki/Total_dissolved_solids


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## rjfurbank (Jan 21, 2008)

I found this online somewhere and use it as a guide. You'll need to research the different localities you reference. I know that some areas of the Amazon can have TDS very low (~0).

0 - 4 dH, 0 - 70 ppm : very soft 
4 - 8 dH, 70 - 140 ppm : soft 
8 - 12 dH, 140 - 210 ppm : medium hard 
12 - 18 dH, 210 - 320 ppm : fairly hard 
18 - 30 dH, 320 - 530 ppm : hard 
higher : liquid rock (Lake Malawi and Los Angeles, CA)


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## HeyPK (Jan 23, 2004)

Dissolved solids are usually meant to be ionic compounds and are measured by a conductivity meter. Usually total dissolved solids are expressed as though everything were calcium carbonate.


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## bartoli (May 8, 2006)

joshvito said:


> What I would like to know is if my water is hard or soft depending on my reading on the TDS meter.


TDS measures the impurity of water. However, not everything that contribute to water impurity affect water hardness. Therefore, looking at a TDS reading, you _cannot reliably_ tell how hard or soft is the water.



rjfurbank said:


> I found this online somewhere and use it as a guide. You'll need to research the different localities you reference. I know that some areas of the Amazon can have TDS very low (~0).
> 
> 0 - 4 dH, 0 - 70 ppm : very soft
> 4 - 8 dH, 70 - 140 ppm : soft
> ...


Note that the above ppm measurements are about those substances that contribute to water hardness. But the ppm in a TDS is about all non-H2O substances dissolved in water (some of them may or may not affect water hardness).


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## HeyPK (Jan 23, 2004)

To check your water hardness, the best thing to do is get a kit that measures GH (calcium and magnesium ion content) and KH (alkalinity---usually is a measure of bicarbonate ion content). The best measure of hardness of the two is GH, which relates to the amount of soap necessary to get a lather.


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