Speaking with “experts” there is a wide variety of opinion on what constitutes “hard water.” Because it is the precise mixture of minerals dissolved in the water, together with the water's pH and temperature, that determines the behavior of the hardness, a single-number scale does not adequately describe hardness. Descriptions of hardness correspond roughly with ranges of mineral concentrations. Wikipedia defines degrees of hardness as follows:
| Soft: | 0-60 mg/L |
|---|---|
| Moderately hard: | 61-120 mg/L |
| Hard: | 121-180 mg/L |
| Very hard: | >181 mg/L |
* Note that mg/L and PPM are roughly equivalent. Example 100 mg/L = 100.1142303 PPM
* A French degree (°fH or °f) is defined as 10 mg/L CaCO3, equivalent to 10 ppm.(A GRAIN = 17.1 ppm or 17.1 mg/L)
The laboratory that we use for water samples suggests “Normal Water” is 70 PPM or less and that at 100 PPM you would probably start to see spotting. Below 70 PPM you would not need a softener. Our normal filters and use of our soap concentrate further assist in reducing spotting so one may wish to not install a softener until a level of 100 PPM appear. As noted in our meeting, we recommend washing during the hours of darkness also. Note that Pool dealers suggest that water above 200 PPM needs to be treated for hard water to avoid spotting.
1. Calcium and Magnesium are important and standard testing addresses both in the hardness readings.
We also like to provide input to designers of solar panel layouts if certain conditions exist. For ground arrays for example, we want to make sure that no irrigation systems will spray water onto the panels. Unfiltered irrigation water sprayed onto solar panels over time may create calcium spotting and reduce output or destroy a solar panel through “hot spotting.” Water flow onto panels must be properly directed in the design to avoid creating hotspots.
For our projects we normally send a water sample to a lab and request a complete metals analysis of the sample. A report is then sent to us. This report aids in determining the correct filtration needed at a site.
Hardness of water is the combination of both Calcium and Magnesium together.
* Note: Because water is potable does NOT mean that it is soft water. Hard water is normally fine for human consumption but not good for spraying on solar panels, cars, windows etc.
| Water Hardness Scale | ||
|---|---|---|
| Grains Per Gallon | Milligrams Per Liter (mg/L)or Parts Per Million (ppm) | Classification |
| less than 1.0 | less than 17.1 | Soft |
| 1.0 - 3.5 | 17.1 - 60 | Slightly Hard |
| 3.5 - 7.0 | 60 - 120 | Moderately Hard |
| 7.0 - 10.5 | 120 - 180 | Hard |
| over 10.5 | over 180 | Very Hard |
1 ppm = 1 mg/L CaCO3
1 ppm = 0.058 grains/US gallon
1 ppm = 0.07 Clark degrees
1 ppm = 0.10 French degrees
1 ppm = 0.056 German degrees
1 French degree = 1 hydrotimetric degree
1 Clark degree = 1 grain / Imperial gallon as calcium carbonate
1 French degree = 1 part / 100,000 calcium carbonate
1 German degree = 1 part / 100,000 calcium oxide
1 grain/US gallon = 17.1 ppm
1 grain/US gallon = 1.20 Clark degrees
1 grain/US gallon = 1.71 French degrees
1 grain/US gallon = 0.958 German degrees
