Hard water is water that has a high mineral content (contrast with soft water). Hard water usually consists of calcium (Ca2+), magnesium (Mg2+) ions, and possibly other dissolved compounds such as bicarbonates and sulfates. Calcium usually enters the water as either calcium carbonate (CaCO3), in the form of limestone and chalk, or calcium sulfate (CaSO4), in the form of other mineral deposits. The predominant source of magnesium is dolomite (CaMg(CO3)2). Hard water is generally not harmful and according to WHO “There does not appear to be any convincing evidence that water hardness causes adverse health effects in humans”
Although, when we think about touristic settings, it can wreck havoc.
If we focus on swimming pools, high water hardness can effect pool water in several fundamental ways:
- It can cause changes in water appearance; water can become more turbid, or cloudy (milky) and with this unappealing to the bathers
- Visual esthetic of your pool can be affected in terms of scaling causing white residue left on ladders, pool decks and other surfaces.
- Damage to the functionality of equipment; scaling can cause clogging and blocking the flow of water in and out of the pool
- Hard water makes it even more tricky to achieve proper water parameter balance (pH, alkalinity, chlorine) and results in higher consumption of chemicals
In the following equilibrium reaction we can observe the dissolving and formation of calcium carbonate and calcium bicarbonate (on the right):
CaCO3 (s) + CO2 (aq) + H2O (l) ⇌ Ca2+ (aq) + 2 HCO−3 (aq)
Ions causing permanent hardness of water can be removed using a water softener, or ion-exchange column.
| Classification | hardness in mg-CaCO3/L | hardness in mmol/L | hardness in dGH/°dH | hardness in ppm |
|---|---|---|---|---|
|
Soft
|
0–60 |
0–0.60 |
0–3.37 |
0–60 |
|
Moderately hard |
61–120 |
0.61–1.20 |
3.38–6.74 |
61–120 |
|
Hard |
121–180 |
1.21–1.80 |
6.75–10.11 |
121–180 |
|
Very hard |
≥ 181 |
≥ 1.81 |
≥ 10.12 |
≥ 181 |
How to measure water hardness?
There are several methods available, from fast checking test kits, photometers to titration systems.
HANNA has developed a new “easy-to-use” solution for testing as an alternative to chemical test kits.
Hardness Low Range Checker - Checker®HC HI735
Features at-a-glance:
- Easier to use and more accurate than chemical test kits
- Dedicated to a single parameter
- Small size, big convenience
- Ideal for: Drinking and process water, heating and cooling systems, swimming pools and spas.
The HI735 Checker®HC (Handheld Colorimeter) is a simple, accurate, and cost effective way to measure total hardness. Designed as a more accurate alternative to chemical test kits, the HI735 provides quick, accurate results in a few easy steps. Our Total Hardness Low Range handheld checker offers you a middle ground between advanced instrumentation and your typical chemical test kit.
Standard test kits have limited accuracy since they rely upon the human eye to match colors. Our handheld colorimeter eliminates the hassle of matching to a color chart by providing a direct Total Hardness Low Range result digitally.
- Range: 0 to 350 ppm (mg/L) as CaCO₃
- Get simple results with easy one-button operation.
- Don’t waste time matching to a color chart anymore, get direct results quickly.
Total Hardness Portable Photometer – HI97735
The HI97735 Total Hardness Photometer combines accuracy and ease of use in a simple, portable design. The advanced optical system provides lab-quality accuracy while its user-friendly design is easy for any user making it the perfect photometer for your water quality testing needs. The HI97735 meter measures total hardness in water samples up to 750 mg/L (ppm) CaCO3.
- No warm up time needed before taking a measurement.
- Tutorial mode for easy step-by-step instructions.
- CAL Check for performance verification and calibration
- Easy navigation between chemical forms with a press-of- a-button:
- mg/L (ppm)
- French degrees (°f)
- German degrees (°dH)
- English degrees (°E)
It’s available in 2 versions
HI97735 & HI97735C
- Sample cuvette (2 pcs.)
- Sample cuvette cap (2 pcs.)
- Plastic stopper (2 pcs.)
- 1.5V AA Alkaline batteries
- Instruction manual
- Meter quality certificate
- Sample cuvette (2 pcs.)
- Sample cuvette cap (2 pcs.)
- Plastic stopper (2 pcs.)
- HI97735A – CAL CheckCuvette A
- HI97735B – CAL Check Cuvette B for Total Hardness LR, MR, HR
- Cloth for wiping cuvettes
- Scissors
- 1.5V AA Alkaline batteries
- Instruction manual
- Meter quality certificate
- CAL Check standard certificate
Reagents & ranges guidelines:
HI93735-00 (100 tests) LR – low range – 0 do 250 mg/L (ppm) CaCO₃; 0-14dH
HI93735-01 (100 tests) MR – middle range – 200 do 500 mg/L (ppm) CaCO₃; 11-28dH
HI93735-02 (100 tests) HR – high range – 400 do 750 mg/L (ppm) CaCO₃; 22-42 dH
*also available as full set HI97735-0 (LR+MR+HR)
Author: Nives Vinceković Budor,mag.ing.chem.ing.
