# How Do I Work Out K/Mg/Ca in Tap Water?



## Superman (30 Oct 2009)

I'm looking to reclac my DIY-EI mix and I wondered how someone can work out the K, Mg and Ca in the tap water from the following report:
http://www.stwater.co.uk/upload/pdf/ZGL ... 0South.pdf

I'm totally lost.

Any help would be greatly appreciated.


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## Superman (30 Oct 2009)

I found a page that does something to get the Ca http://www.cactus2000.de/uk/unit/masswas.shtml


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## Superman (31 Oct 2009)

Anyone?


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## JamesC (31 Oct 2009)

Doesn't really tell you much. Is there not another report. My Thames Water report is slpit in two halves. One the same as your one and also another report that deals with water hardness.

James


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## Superman (31 Oct 2009)

There was this info also

http://www.stwater.co.uk/server.php?pos ... itySubmit=


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## Superman (1 Nov 2009)

Superman said:
			
		

> There was this info also
> 
> http://www.stwater.co.uk/server.php?pos ... itySubmit=



Sorry, I wasn't at home so couldn't copy the details on that link, but here it is...


```
---Analysis-------Typical Value------UK/European Limit------Units------
Hardness Level    Moderately hard	No Standard Applies
Hardness Clark    13.26 				No Standard Applies 	Degrees Clark
Hardness French   18.95 				No Standard Applies 	French Degrees
Hardness German   10.61 				No Standard Applies 	German Degrees
```


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## dw1305 (12 Nov 2009)

Hi Superman,
The water parameters don't look to bad, even though there are traces of ammonia  it doesn't look like they use chloramine as a disinfectant. The parameters for all the organic pollutants are all reasonable, suggesting to be that your water is largely borehole water from some fairly deep  limestone aquifer. You have a small amount of sodium which will contribute to the TDS, but not a lot else other than dissolved calcium carbonate (I've ignored magnesium, as there aren't any magnesium rich rocks locally, but this wouldn't be true if you lived on "the Lizard" in Cornwall for example ). This water is fine unless you want to keep "black water" fish and plants, particularly if you could mix it with some R.O. or rainwater (which will have much lower conductivity and hardness ).

The figures of the most interest to you are:
conductivity in microS.
&
Hardness German.

I'll ignore pH as it is a bit of a moveable feast, but your water is well buffered so you would need a lot of weak acid (carbonic from CO2 for example or a small amount of HCl) to reduce the pH significantly below pH7.

*Conductivity*
Your mean conductivity is 462 microS, this is 296 ppm TDS.

To convert TDS to conductivity in micro S.
64 ppm TDS = conductivity of 100 micro S, and 100 ppm TDS = 156 micro S.

*Hardness*
Your hardness is 10.61 German or 193 ppm calcium carbonate and officially "slightly hard".

I've put the workings and some units below:
Your hardness is mainly a measure of the calcium carbonate (the lime(stone), chalk or scale) content. The equilibrium reaction is:

CaCO3(solid) + H2CO3(aq. in solution) â‡‹ Ca2+(aq) + 2HCO3-(aq) (exactly same for Mg2+ as well, so both Ca and Mg are usually added together and expressed just as calcium)

As you heat the water CO2 becomes less soluble (it's not in the equation as CO2, but bicarbonate is - 2 x HCO3-) which moves the equation from right to left (less CO2 means less bicarbonate ions HCO3- to balance the Ca2+ ions), Ca2+ can't remain in solution and are precipitated out as the "scale" (CaCO3) in your kettle, immersion heater etc.

Units
Parts per million (ppm) is the same as milligrams per litre (1000 cm3 in a litre, which for water weighs 1000g (a kilogram), 1000 milligrams in 1cm3 which weighs 1 gram).

Parts per billion (ppb) is micrograms per litre (1000 micrograms to the milligram).

mmol/L (millimoles per litre)
One millimole of calcium (either Ca2+ or CaCO3) per litre of water corresponds to a hardness of 100 ppm or 5.61 dGH, since the molar mass of calcium carbonate is 100g/mol.

(Ca has a RAM of 40, C = 12 and O = 16, CaCO3 = 40 + 12 + 48(16 x 3) = 100).

100g in 1 litre is a molar solution of calcium carbonate (40% Ca), and 0.1g per litre a millimolar solution.

1 dH is "One degree German" and defined as 10 milligrams of calcium oxide (CaO) per litre of water. This is equivalent to 17.85 milligrams of calcium carbonate per litre of water, or 17.85 ppm. (look up American, Clark, French degrees etc. on Wikipedia for a conversion).

As an example my tap water (Corsham, Wilts - SN13 9AR), so about 40 miles to the other side of the Cotswolds is:

Calcium (milligrams per litre) 119 (298 x 40% = 119)
Calcium carbonate (milligrams per litre) 298
Degrees German (ÂºdH) 16.7 (16.7 x 17.85 = 298)
Degrees French (Âºf) 30
Degrees Clark 21
Sodium (milligrams per litre) 22
Conductivity 615 micro S(iemens)

Descriptions of hardness correspond roughly with these ranges of mineral (Ca, Mg) concentrations: (pinched straight from Wikipedia)

* Very soft: 0-70 ppm, 0-4 dGH
* Soft: 70-140 ppm, 4-8 dGH
* Slightly hard: 140-210 ppm, 8-12 dGH
* Moderately hard: 210-320 ppm, 12-18 dGH
* Hard: 320-530 ppm, 18-30 dGH
* Very hard >530 ppm, >30 dGH

Making my water officially "moderately hard". However I've tested my tap water a couple of times and the conductivity was about 800 microS, suggesting that the value may be quite variable around the average figure given.....

cheers Darrel


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## dw1305 (12 Nov 2009)

Hi all,
Should also have said you are unlikely to have significant levels of potassium (K) in your water for the same geological reasons as for magnesium (Mg).
cheers Darrel


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