High Hardness but Low TDS?

Hello All,

How can water have a high hardness but a low TDS?

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• Total Dissolved Solids (TDS)

13 Answers

1. It is possible in rare circumstances to have a hardness that is higher than TDS, due to the difference in the reporting units. Hardness is traditionally reported in "mg/L as CaCO3", while TDS is often reporting in mg/L. The measurement methods are also different, with hardness usually being determined by titration or ICP-AES, and TDS often being determined by dry residue. 

    

   For example, a water sample that contains only 1 mmol/L of MgF2 (magnesium fluoride) would have a TDS of 62 mg/L, but a hardness of 100 mg/L as CaCO3. 

   1 Comment

   1. Thanks.

2. Hardness can not be greater than TDS.

3. Absolutely possible.... hardness due to Ca and Mg ions... and Turbidity due to light scattering because of fine suspended solid...

4. Of course.  It is a matter of the definition of HIGH in each case. High hardness is considered to be over about 120 mg/L as calcium carbonate. High TDS is considered to occur at least at above 500 mg/L but it can go to well over 1000 mg/L.

5. Hi...Unit of Total Hardness (TH) mainly is Ca++ and Mg++  are mg per liter as CaCO3...but TDS is all every element that soluted in water with unit mg per liter. Normally TDS is higher than TH. But this is a good and interesting question if your measuring is correct and your equipment have been calibrate.

6. Hi, it may simply be a confusion between their units! TDS should always be higher than TH if you consider mg of solids. But there is different units for TH that you should take care when you compare with TDS.

7. Total hardness includes Ca & Mg ions.Interference of iron may increase TH whereas TDS includes all dissolved ions .Sodium & chlorides ions presence in water increase the TDS levels. The conclusion is that chlorides ions conc. is directly influencing TDS low conc of which may lower the TDS but has no impact on TH.

8. Hardness is a part from TDS, so TDS can not lower than hardness.

9. Yes. If there is a CaCO3 stone into deionized water, for example. 

10. Total hardness in water is the added amount of calcium and magnesium ions. Total dissolved solids also involves all dissolved solids/ions in the your water thus it also includes calcium and magnesium. How low is the TDS acceptable?

11. In water and wastewater treatment there are several questions that are not binary and answers need to be more consistant. Please formulate it with more information and why it happens. Regards 

12. Hi hardness means high calcium and magnesium or maybe iron.....TDS means total dissolved solids including all cations and anions....So typically your water can high of the former but overall it may have low or under norms in terms of total TDS..

13. What numbers are high hat's low, pls specify better

     

    1 Comment

    1. Hardness is a sub set of TDS, when insoluble(suspended) hardness is included as dissolved solids thru elemental analysis, the proportion changes.