Ions	Concentration		Weight [g/mole]	Charge	mg/meq	meq/L
Ca2+		mg/L g/m3 ppm eq/L meq/L mol/L mmol/L	40,1	2	20,1
Mg2+		mg/L g/m3 ppm eq/L meq/L mol/L mmol/L	24,3	2	12,2
Na+		mg/L g/m3 ppm eq/L meq/L mol/L mmol/L	23,0	1	23,0
K+		mg/L g/m3 ppm eq/L meq/L mol/L mmol/L	39,1	1	39,1
HCO3-		mg/L g/m3 ppm eq/L meq/L mol/L mmol/L	61,0	1	61,0
SO42-		mg/L g/m3 ppm eq/L meq/L mol/L mmol/L	96,1	2	48,1
Cl-		mg/L g/m3 ppm eq/L meq/L mol/L mmol/L	35,5	1	35,5
NO3-		mg/L g/m3 ppm eq/L meq/L mol/L mmol/L	62,0	1	62,0

	meq/L
	meq/L
Percent difference	%
Interpretation of the percent difference

The acceptance criteria for the percent difference are as given below:

meq/L	Acceptable difference
0 - 3.0	± 0.2 %
3.0 - 10.0	± 2%
10  - 800	± 5%

The percent difference is calculated with the following formula:

Percent difference

The equivalent weight (g/eq or mg/meq) of a compound is defined as:

Equivalent weight=

where:
	M=	molecular weight, g
	Z=	charge

Remark: The table above shows only the ions that are usually present in tap water. If you have for example Silicates and Fluorides in your water, the judgment on the analysis accuracy is not totally correct.