Tap water – easy ways to check Water Total Hardness

Category: Water | Tags:
Hard water is one
of the most common concerns in every household.
The ‘hardness’ of your water depends on naturally occurring water mineralization, mostly caused by minerals as calcium and magnesium.
Hard water depends on local geology – water hardness varies widely throughout the world.
What is “hard water”?
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”.
Hard water is mostly causing problems in households in terms of damaging appliances like dishwasher, washing machine but also smaller devices water kettles and coffee makers.
Hard water forms deposits that clog plumbing. These deposits, called “scale”, are composed mainly of calcium carbonate (CaCO3), magnesium hydroxide (Mg(OH)2), and calcium sulfate (CaSO4).Calcium and magnesium carbonates tend to be deposited as off-white solids on the inside surfaces of pipes and heat exchangers.
The resulting build-up of scale restricts the flow of water in pipes. In boilers, the deposits impair the flow of heat into water, reducing the heating efficiency and allowing the metal boiler components to overheat. In a pressurized system, this overheating can lead to failure of the boiler.
In the following equilibrium reaction we can observe
the dissolving and formation of calcium carbonate and
calcium bicarbonate (on the right):
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
Moderately hard
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
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
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)

● Press the

key and use the functional keys to select Chemical Form.
● Use the functional keys and press Select to change the displayed chemical form to       French degreess (˚f), German degrees (˚dH) and English degrees (˚E).

● Press

to return to the mesurement screen.
It’s available in 2 versions HI97735 & HI97735C:


Each HI97735 is delivered in a cardboard box and is supplied with:
  • Sample cuvette (2 pcs.)
  • Sample cuvette cap (2 pcs.)
  • Plastic stopper (2 pcs.)
  • 1.5V AA Alkaline batteries
  • Instruction manual
  • Meter quality certificate


Each HI97735C is delivered in a rugged carrying case and is supplied with:
  • 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
&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)
Nives Vinceković Budor
With Great Product Come Great Results





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